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 $56.49   11.516%   $62.9954   $63.00   $63.00   $63.00  
  Purchase #2 $96.25   10.608%   $106.4602   $106.46   $106.45   $106.50  
  Purchase #3 $234.67   12.290%   $263.5109   $263.51   $263.50   $263.50  
  Purchase #4 $87.74   9.376%   $95.9665   $95.97   $95.95   $96.00  
  Purchase #5 $87.49   12.385%   $98.3256   $98.33   $98.35   $98.30  
  Purchase #6 $232.81   9.847%   $255.7348   $255.73   $255.75   $255.70  
  Purchase #7 $59.98   7.357%   $64.3927   $64.39   $64.40   $64.40  
  7 purchase totals = $855.43       $947.3861   $947.39   $947.40   $947.40