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 $76.49   11.132%   $85.0049   $85.00   $85.00   $85.00  
  Purchase #2 $214.37   7.234%   $229.8775   $229.88   $229.90   $229.90  
  Purchase #3 $161.57   12.492%   $181.7533   $181.75   $181.75   $181.80  
  Purchase #4 $39.56   3.808%   $41.0664   $41.07   $41.05   $41.10  
  Purchase #5 $174.72   11.382%   $194.6066   $194.61   $194.60   $194.60  
  Purchase #6 $154.66   3.205%   $159.6169   $159.62   $159.60   $159.60  
  Purchase #7 $192.85   4.546%   $201.617   $201.62   $201.60   $201.60  
  7 purchase totals = $1,014.22       $1,093.5426   $1,093.55   $1,093.50   $1,093.60