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 $84.96   9.192%   $92.7695   $92.77   $92.75   $92.80  
  Purchase #2 $138.44   8.510%   $150.2212   $150.22   $150.20   $150.20  
  Purchase #3 $160.91   6.825%   $171.8921   $171.89   $171.90   $171.90  
  Purchase #4 $250.77   12.287%   $281.5821   $281.58   $281.60   $281.60  
  Purchase #5 $81.95   10.315%   $90.4031   $90.40   $90.40   $90.40  
  Purchase #6 $154.38   5.868%   $163.439   $163.44   $163.45   $163.40  
  Purchase #7 $15.45   7.643%   $16.6308   $16.63   $16.65   $16.60  
  7 purchase totals = $886.86       $966.9378   $966.93   $966.95   $966.90