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 $213.84   10.642%   $236.5969   $236.60   $236.60   $236.60  
  Purchase #2 $211.55   11.257%   $235.3642   $235.36   $235.35   $235.40  
  Purchase #3 $7.49   8.556%   $8.1308   $8.13   $8.15   $8.10  
  Purchase #4 $124.45   11.569%   $138.8476   $138.85   $138.85   $138.80  
  Purchase #5 $119.42   9.607%   $130.8927   $130.89   $130.90   $130.90  
  Purchase #6 $45.68   7.192%   $48.9653   $48.97   $48.95   $49.00  
  Purchase #7 $146.68   6.556%   $156.2963   $156.30   $156.30   $156.30  
  7 purchase totals = $869.11       $955.0938   $955.10   $955.10   $955.10