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 $150.79   7.658%   $162.3375   $162.34   $162.35   $162.30  
  Purchase #2 $209.32   11.843%   $234.1098   $234.11   $234.10   $234.10  
  Purchase #3 $41.76   8.590%   $45.3472   $45.35   $45.35   $45.30  
  Purchase #4 $245.72   7.418%   $263.9475   $263.95   $263.95   $263.90  
  Purchase #5 $217.79   6.852%   $232.713   $232.71   $232.70   $232.70  
  Purchase #6 $47.32   3.528%   $48.9894   $48.99   $49.00   $49.00  
  Purchase #7 $44.46   10.211%   $48.9998   $49.00   $49.00   $49.00  
  7 purchase totals = $957.16       $1,036.4442   $1,036.45   $1,036.45   $1,036.30