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 $224.40   13.198%   $254.0163   $254.02   $254.00   $254.00  
  Purchase #2 $153.60   12.871%   $173.3699   $173.37   $173.35   $173.40  
  Purchase #3 $25.70   3.439%   $26.5838   $26.58   $26.60   $26.60  
  Purchase #4 $208.53   12.119%   $233.8018   $233.80   $233.80   $233.80  
  Purchase #5 $152.55   12.726%   $171.9635   $171.96   $171.95   $172.00  
  Purchase #6 $97.38   5.871%   $103.0972   $103.10   $103.10   $103.10  
  Purchase #7 $74.33   3.770%   $77.1322   $77.13   $77.15   $77.10  
  7 purchase totals = $936.49       $1,039.9647   $1,039.96   $1,039.95   $1,040.00