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 $58.90   8.670%   $64.0066   $64.01   $64.00   $64.00  
  Purchase #2 $55.77   3.363%   $57.6455   $57.65   $57.65   $57.60  
  Purchase #3 $234.52   8.802%   $255.1625   $255.16   $255.15   $255.20  
  Purchase #4 $12.45   5.660%   $13.1547   $13.15   $13.15   $13.20  
  Purchase #5 $149.49   13.403%   $169.5261   $169.53   $169.55   $169.50  
  Purchase #6 $34.55   10.759%   $38.2672   $38.27   $38.25   $38.30  
  Purchase #7 $151.84   5.253%   $159.8162   $159.82   $159.80   $159.80  
  7 purchase totals = $697.52       $757.5788   $757.59   $757.55   $757.60