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 $217.79   3.186%   $224.7288   $224.73   $224.75   $224.70  
  Purchase #2 $151.73   10.786%   $168.0956   $168.10   $168.10   $168.10  
  Purchase #3 $9.52   13.653%   $10.8198   $10.82   $10.80   $10.80  
  Purchase #4 $91.36   4.808%   $95.7526   $95.75   $95.75   $95.80  
  Purchase #5 $36.31   9.708%   $39.835   $39.84   $39.85   $39.80  
  Purchase #6 $245.85   5.570%   $259.5438   $259.54   $259.55   $259.50  
  Purchase #7 $208.99   13.102%   $236.3719   $236.37   $236.35   $236.40  
  7 purchase totals = $961.55       $1,035.1475   $1,035.15   $1,035.15   $1,035.10