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 $127.48   7.323%   $136.8154   $136.82   $136.80   $136.80  
  Purchase #2 $229.94   10.613%   $254.3435   $254.34   $254.35   $254.30  
  Purchase #3 $41.93   10.815%   $46.4647   $46.46   $46.45   $46.50  
  Purchase #4 $140.81   13.265%   $159.4884   $159.49   $159.50   $159.50  
  Purchase #5 $129.39   10.735%   $143.28   $143.28   $143.30   $143.30  
  Purchase #6 $76.41   10.834%   $84.6883   $84.69   $84.70   $84.70  
  Purchase #7 $41.74   11.697%   $46.6223   $46.62   $46.60   $46.60  
  7 purchase totals = $787.70       $871.7026   $871.70   $871.70   $871.70