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 $227.69   11.354%   $253.5419   $253.54   $253.55   $253.50  
  Purchase #2 $161.34   3.814%   $167.4935   $167.49   $167.50   $167.50  
  Purchase #3 $182.59   10.172%   $201.1631   $201.16   $201.15   $201.20  
  Purchase #4 $94.73   8.295%   $102.5879   $102.59   $102.60   $102.60  
  Purchase #5 $66.64   4.643%   $69.7341   $69.73   $69.75   $69.70  
  Purchase #6 $35.56   10.556%   $39.3137   $39.31   $39.30   $39.30  
  Purchase #7 $138.86   10.244%   $153.0848   $153.08   $153.10   $153.10  
  7 purchase totals = $907.41       $986.9190   $986.90   $986.95   $986.90