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 $41.39   7.830%   $44.6308   $44.63   $44.65   $44.60  
  Purchase #2 $65.31   4.245%   $68.0824   $68.08   $68.10   $68.10  
  Purchase #3 $43.48   5.491%   $45.8675   $45.87   $45.85   $45.90  
  Purchase #4 $48.92   13.131%   $55.3437   $55.34   $55.35   $55.30  
  Purchase #5 $228.93   11.164%   $254.4877   $254.49   $254.50   $254.50  
  Purchase #6 $233.76   11.671%   $261.0421   $261.04   $261.05   $261.00  
  Purchase #7 $11.95   13.659%   $13.5823   $13.58   $13.60   $13.60  
  7 purchase totals = $673.74       $743.0365   $743.03   $743.10   $743.00