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 $66.29   10.437%   $73.2087   $73.21   $73.20   $73.20  
  Purchase #2 $164.54   8.297%   $178.1919   $178.19   $178.20   $178.20  
  Purchase #3 $219.53   8.618%   $238.4491   $238.45   $238.45   $238.40  
  Purchase #4 $32.33   8.120%   $34.9552   $34.96   $34.95   $35.00  
  Purchase #5 $56.27   5.580%   $59.4099   $59.41   $59.40   $59.40  
  Purchase #6 $212.56   13.815%   $241.9252   $241.93   $241.95   $241.90  
  Purchase #7 $121.75   7.819%   $131.2696   $131.27   $131.25   $131.30  
  7 purchase totals = $873.27       $957.4096   $957.42   $957.40   $957.40