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 $217.94   5.627%   $230.2035   $230.20   $230.20   $230.20  
  Purchase #2 $120.47   4.312%   $125.6647   $125.66   $125.65   $125.70  
  Purchase #3 $58.31   4.437%   $60.8972   $60.90   $60.90   $60.90  
  Purchase #4 $79.67   7.741%   $85.8373   $85.84   $85.85   $85.80  
  Purchase #5 $175.96   13.378%   $199.4999   $199.50   $199.50   $199.50  
  Purchase #6 $166.81   13.106%   $188.6721   $188.67   $188.65   $188.70  
  Purchase #7 $70.84   8.545%   $76.8933   $76.89   $76.90   $76.90  
  7 purchase totals = $890.00       $967.6680   $967.66   $967.65   $967.70