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 $55.67   5.538%   $58.753   $58.75   $58.75   $58.80  
  Purchase #2 $187.59   3.172%   $193.5404   $193.54   $193.55   $193.50  
  Purchase #3 $180.80   11.678%   $201.9138   $201.91   $201.90   $201.90  
  Purchase #4 $225.90   13.296%   $255.9357   $255.94   $255.95   $255.90  
  Purchase #5 $223.76   6.450%   $238.1925   $238.19   $238.20   $238.20  
  Purchase #6 $244.42   8.219%   $264.5089   $264.51   $264.50   $264.50  
  Purchase #7 $158.57   13.813%   $180.4733   $180.47   $180.45   $180.50  
  7 purchase totals = $1,276.71       $1,393.3176   $1,393.31   $1,393.30   $1,393.30