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 $200.80   12.810%   $226.5225   $226.52   $226.50   $226.50  
  Purchase #2 $36.65   4.452%   $38.2817   $38.28   $38.30   $38.30  
  Purchase #3 $11.34   10.677%   $12.5508   $12.55   $12.55   $12.60  
  Purchase #4 $158.68   7.124%   $169.9844   $169.98   $170.00   $170.00  
  Purchase #5 $113.95   10.547%   $125.9683   $125.97   $125.95   $126.00  
  Purchase #6 $163.60   6.111%   $173.5976   $173.60   $173.60   $173.60  
  Purchase #7 $202.72   6.580%   $216.059   $216.06   $216.05   $216.10  
  7 purchase totals = $887.74       $962.9643   $962.96   $962.95   $963.10