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 $86.70   10.369%   $95.6899   $95.69   $95.70   $95.70  
  Purchase #2 $51.53   6.847%   $55.0583   $55.06   $55.05   $55.10  
  Purchase #3 $200.98   7.447%   $215.947   $215.95   $215.95   $215.90  
  Purchase #4 $35.87   11.818%   $40.1091   $40.11   $40.10   $40.10  
  Purchase #5 $167.70   12.261%   $188.2617   $188.26   $188.25   $188.30  
  Purchase #6 $139.30   11.595%   $155.4518   $155.45   $155.45   $155.50  
  Purchase #7 $24.40   11.257%   $27.1467   $27.15   $27.15   $27.10  
  7 purchase totals = $706.48       $777.6645   $777.67   $777.65   $777.70