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 $64.42   6.349%   $68.51   $68.51   $68.50   $68.50  
  Purchase #2 $210.56   4.442%   $219.9131   $219.91   $219.90   $219.90  
  Purchase #3 $46.67   7.348%   $50.0993   $50.10   $50.10   $50.10  
  Purchase #4 $161.56   8.859%   $175.8726   $175.87   $175.85   $175.90  
  Purchase #5 $53.82   12.477%   $60.5351   $60.54   $60.55   $60.50  
  Purchase #6 $163.36   10.530%   $180.5618   $180.56   $180.55   $180.60  
  Purchase #7 $210.25   7.243%   $225.4784   $225.48   $225.50   $225.50  
  7 purchase totals = $910.64       $980.9703   $980.97   $980.95   $981.00