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 $125.53   4.770%   $131.5178   $131.52   $131.50   $131.50  
  Purchase #2 $221.55   6.306%   $235.5209   $235.52   $235.50   $235.50  
  Purchase #3 $106.73   10.806%   $118.2632   $118.26   $118.25   $118.30  
  Purchase #4 $192.66   10.788%   $213.4442   $213.44   $213.45   $213.40  
  Purchase #5 $106.55   6.791%   $113.7858   $113.79   $113.80   $113.80  
  Purchase #6 $244.84   6.622%   $261.0533   $261.05   $261.05   $261.10  
  Purchase #7 $27.57   10.537%   $30.4751   $30.48   $30.50   $30.50  
  7 purchase totals = $1,025.43       $1,104.0603   $1,104.06   $1,104.05   $1,104.10