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 $212.68   5.314%   $223.9818   $223.98   $224.00   $224.00  
  Purchase #2 $83.86   12.509%   $94.35   $94.35   $94.35   $94.40  
  Purchase #3 $87.44   13.136%   $98.9261   $98.93   $98.95   $98.90  
  Purchase #4 $156.87   7.776%   $169.0682   $169.07   $169.05   $169.10  
  Purchase #5 $58.83   6.534%   $62.674   $62.67   $62.65   $62.70  
  Purchase #6 $42.27   5.793%   $44.7187   $44.72   $44.70   $44.70  
  Purchase #7 $41.83   10.533%   $46.236   $46.24   $46.25   $46.20  
  7 purchase totals = $683.78       $739.9548   $739.96   $739.95   $740.00