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 $232.74   7.758%   $250.796   $250.80   $250.80   $250.80  
  Purchase #2 $24.38   10.448%   $26.9272   $26.93   $26.95   $26.90  
  Purchase #3 $71.40   4.155%   $74.3667   $74.37   $74.35   $74.40  
  Purchase #4 $18.78   6.613%   $20.0219   $20.02   $20.00   $20.00  
  Purchase #5 $23.99   4.120%   $24.9784   $24.98   $25.00   $25.00  
  Purchase #6 $193.46   6.632%   $206.2903   $206.29   $206.30   $206.30  
  Purchase #7 $173.52   9.544%   $190.0807   $190.08   $190.10   $190.10  
  7 purchase totals = $738.27       $793.4612   $793.47   $793.50   $793.50