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 $156.54   8.645%   $170.0729   $170.07   $170.05   $170.10  
  Purchase #2 $209.53   12.132%   $234.9502   $234.95   $234.95   $235.00  
  Purchase #3 $62.80   8.239%   $67.9741   $67.97   $67.95   $68.00  
  Purchase #4 $152.54   11.450%   $170.0058   $170.01   $170.00   $170.00  
  Purchase #5 $163.65   13.187%   $185.2305   $185.23   $185.25   $185.20  
  Purchase #6 $37.39   9.589%   $40.9753   $40.98   $41.00   $41.00  
  Purchase #7 $25.88   6.208%   $27.4866   $27.49   $27.50   $27.50  
  7 purchase totals = $808.33       $896.6954   $896.70   $896.70   $896.80