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 $188.73   11.139%   $209.7526   $209.75   $209.75   $209.80  
  Purchase #2 $29.33   12.447%   $32.9807   $32.98   $33.00   $33.00  
  Purchase #3 $152.46   13.463%   $172.9857   $172.99   $173.00   $173.00  
  Purchase #4 $126.47   10.861%   $140.2059   $140.21   $140.20   $140.20  
  Purchase #5 $77.97   9.213%   $85.1534   $85.15   $85.15   $85.20  
  Purchase #6 $155.26   3.660%   $160.9425   $160.94   $160.95   $160.90  
  Purchase #7 $197.94   11.119%   $219.9489   $219.95   $219.95   $219.90  
  7 purchase totals = $928.16       $1,021.9697   $1,021.97   $1,022.00   $1,022.00