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 $230.94   12.791%   $260.4795   $260.48   $260.50   $260.50  
  Purchase #2 $179.81   9.780%   $197.3954   $197.40   $197.40   $197.40  
  Purchase #3 $85.43   10.183%   $94.1293   $94.13   $94.15   $94.10  
  Purchase #4 $195.45   13.468%   $221.7732   $221.77   $221.75   $221.80  
  Purchase #5 $162.94   7.686%   $175.4636   $175.46   $175.45   $175.50  
  Purchase #6 $240.26   3.182%   $247.9051   $247.91   $247.90   $247.90  
  Purchase #7 $66.44   7.763%   $71.5977   $71.60   $71.60   $71.60  
  7 purchase totals = $1,161.27       $1,268.7438   $1,268.75   $1,268.75   $1,268.80