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 $10.28   6.863%   $10.9855   $10.99   $11.00   $11.00  
  Purchase #2 $143.99   8.399%   $156.0837   $156.08   $156.10   $156.10  
  Purchase #3 $107.35   4.398%   $112.0713   $112.07   $112.05   $112.10  
  Purchase #4 $212.30   10.768%   $235.1605   $235.16   $235.15   $235.20  
  Purchase #5 $91.97   10.248%   $101.3951   $101.40   $101.40   $101.40  
  Purchase #6 $62.68   10.736%   $69.4093   $69.41   $69.40   $69.40  
  Purchase #7 $212.56   10.236%   $234.3176   $234.32   $234.30   $234.30  
  7 purchase totals = $841.13       $919.4230   $919.43   $919.40   $919.50