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 $58.31   12.752%   $65.7457   $65.75   $65.75   $65.70  
  Purchase #2 $33.94   10.283%   $37.4301   $37.43   $37.45   $37.40  
  Purchase #3 $93.96   5.517%   $99.1438   $99.14   $99.15   $99.10  
  Purchase #4 $85.51   3.814%   $88.7714   $88.77   $88.75   $88.80  
  Purchase #5 $240.84   7.786%   $259.5918   $259.59   $259.60   $259.60  
  Purchase #6 $160.73   5.837%   $170.1118   $170.11   $170.10   $170.10  
  Purchase #7 $153.38   4.311%   $159.9922   $159.99   $160.00   $160.00  
  7 purchase totals = $826.67       $880.7868   $880.78   $880.80   $880.70