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 $61.31   12.127%   $68.7451   $68.75   $68.75   $68.70  
  Purchase #2 $118.38   8.462%   $128.3973   $128.40   $128.40   $128.40  
  Purchase #3 $241.52   7.666%   $260.0349   $260.03   $260.05   $260.00  
  Purchase #4 $207.61   12.687%   $233.9495   $233.95   $233.95   $233.90  
  Purchase #5 $239.71   4.435%   $250.3411   $250.34   $250.35   $250.30  
  Purchase #6 $66.38   4.785%   $69.5563   $69.56   $69.55   $69.60  
  Purchase #7 $242.83   3.237%   $250.6904   $250.69   $250.70   $250.70  
  7 purchase totals = $1,177.74       $1,261.7146   $1,261.72   $1,261.75   $1,261.60