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 $208.71   11.354%   $232.4069   $232.41   $232.40   $232.40  
  Purchase #2 $236.95   11.405%   $263.9741   $263.97   $263.95   $264.00  
  Purchase #3 $106.55   12.430%   $119.7942   $119.79   $119.80   $119.80  
  Purchase #4 $72.43   12.182%   $81.2534   $81.25   $81.25   $81.30  
  Purchase #5 $58.83   10.747%   $65.1525   $65.15   $65.15   $65.20  
  Purchase #6 $141.74   4.868%   $148.6399   $148.64   $148.65   $148.60  
  Purchase #7 $56.34   12.368%   $63.3081   $63.31   $63.30   $63.30  
  7 purchase totals = $881.55       $974.5291   $974.52   $974.50   $974.60