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 $59.89   10.259%   $66.0341   $66.03   $66.05   $66.00  
  Purchase #2 $129.72   12.819%   $146.3488   $146.35   $146.35   $146.30  
  Purchase #3 $89.52   8.107%   $96.7774   $96.78   $96.80   $96.80  
  Purchase #4 $91.58   6.138%   $97.2012   $97.20   $97.20   $97.20  
  Purchase #5 $12.76   3.247%   $13.1743   $13.17   $13.15   $13.20  
  Purchase #6 $241.79   5.491%   $255.0667   $255.07   $255.05   $255.10  
  Purchase #7 $246.69   8.377%   $267.3552   $267.36   $267.35   $267.40  
  7 purchase totals = $871.95       $941.9577   $941.96   $941.95   $942.00