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 $114.95   8.785%   $125.0484   $125.05   $125.05   $125.00  
  Purchase #2 $196.49   4.145%   $204.6345   $204.63   $204.65   $204.60  
  Purchase #3 $131.93   13.342%   $149.5321   $149.53   $149.55   $149.50  
  Purchase #4 $92.49   13.582%   $105.052   $105.05   $105.05   $105.10  
  Purchase #5 $157.69   3.253%   $162.8197   $162.82   $162.80   $162.80  
  Purchase #6 $175.99   13.359%   $199.5005   $199.50   $199.50   $199.50  
  Purchase #7 $30.52   11.163%   $33.9269   $33.93   $33.95   $33.90  
  7 purchase totals = $900.06       $980.5141   $980.51   $980.55   $980.40