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 $29.67   12.709%   $33.4408   $33.44   $33.45   $33.40  
  Purchase #2 $113.88   11.477%   $126.95   $126.95   $126.95   $127.00  
  Purchase #3 $61.31   7.623%   $65.9837   $65.98   $66.00   $66.00  
  Purchase #4 $208.54   10.114%   $229.6317   $229.63   $229.65   $229.60  
  Purchase #5 $43.94   5.397%   $46.3114   $46.31   $46.30   $46.30  
  Purchase #6 $182.29   5.251%   $191.862   $191.86   $191.85   $191.90  
  Purchase #7 $163.60   12.524%   $184.0893   $184.09   $184.10   $184.10  
  7 purchase totals = $803.23       $878.2689   $878.26   $878.30   $878.30