Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $160.81   9.570%   $176.1995   $176.20   $176.20   $176.20  
  Purchase #2 $240.39   11.371%   $267.7247   $267.72   $267.70   $267.70  
  Purchase #3 $248.49   12.618%   $279.8445   $279.84   $279.85   $279.80  
  Purchase #4 $215.32   4.118%   $224.1869   $224.19   $224.20   $224.20  
  Purchase #5 $133.51   10.475%   $147.4952   $147.50   $147.50   $147.50  
  Purchase #6 $218.84   11.782%   $244.6237   $244.62   $244.60   $244.60  
  Purchase #7 $201.60   11.549%   $224.8828   $224.88   $224.90   $224.90  
  7 purchase totals = $1,418.96       $1,564.9573   $1,564.95   $1,564.95   $1,564.90