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 $30.84   8.683%   $33.5178   $33.52   $33.50   $33.50  
  Purchase #2 $178.53   9.729%   $195.8992   $195.90   $195.90   $195.90  
  Purchase #3 $66.54   10.439%   $73.4861   $73.49   $73.50   $73.50  
  Purchase #4 $119.65   10.142%   $131.7849   $131.78   $131.80   $131.80  
  Purchase #5 $67.46   3.845%   $70.0538   $70.05   $70.05   $70.10  
  Purchase #6 $236.47   11.287%   $263.1604   $263.16   $263.15   $263.20  
  Purchase #7 $212.51   9.743%   $233.2148   $233.21   $233.20   $233.20  
  7 purchase totals = $912.00       $1,001.1170   $1,001.11   $1,001.10   $1,001.20