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 $78.52   4.691%   $82.2034   $82.20   $82.20   $82.20  
  Purchase #2 $100.95   10.272%   $111.3196   $111.32   $111.30   $111.30  
  Purchase #3 $117.29   8.446%   $127.1963   $127.20   $127.20   $127.20  
  Purchase #4 $75.26   8.591%   $81.7256   $81.73   $81.75   $81.70  
  Purchase #5 $108.65   10.145%   $119.6725   $119.67   $119.65   $119.70  
  Purchase #6 $217.58   10.354%   $240.1082   $240.11   $240.10   $240.10  
  Purchase #7 $24.43   4.699%   $25.578   $25.58   $25.60   $25.60  
  7 purchase totals = $722.68       $787.8036   $787.81   $787.80   $787.80