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 $82.93   10.640%   $91.7538   $91.75   $91.75   $91.80  
  Purchase #2 $249.53   11.405%   $277.9889   $277.99   $278.00   $278.00  
  Purchase #3 $77.38   9.527%   $84.752   $84.75   $84.75   $84.80  
  Purchase #4 $101.47   10.312%   $111.9336   $111.93   $111.95   $111.90  
  Purchase #5 $154.37   5.120%   $162.2737   $162.27   $162.25   $162.30  
  Purchase #6 $164.98   5.455%   $173.9797   $173.98   $174.00   $174.00  
  Purchase #7 $87.50   6.407%   $93.1061   $93.11   $93.10   $93.10  
  7 purchase totals = $918.16       $995.7878   $995.78   $995.80   $995.90