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 $53.33   9.761%   $58.5355   $58.54   $58.55   $58.50  
  Purchase #2 $213.88   13.110%   $241.9197   $241.92   $241.90   $241.90  
  Purchase #3 $231.85   5.450%   $244.4858   $244.49   $244.50   $244.50  
  Purchase #4 $92.31   13.214%   $104.5078   $104.51   $104.50   $104.50  
  Purchase #5 $22.64   8.795%   $24.6312   $24.63   $24.65   $24.60  
  Purchase #6 $48.63   8.839%   $52.9284   $52.93   $52.95   $52.90  
  Purchase #7 $227.99   8.141%   $246.5507   $246.55   $246.55   $246.60  
  7 purchase totals = $890.63       $973.5591   $973.57   $973.60   $973.50