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 $204.94   13.450%   $232.5044   $232.50   $232.50   $232.50  
  Purchase #2 $248.44   7.574%   $267.2568   $267.26   $267.25   $267.30  
  Purchase #3 $89.87   9.508%   $98.4148   $98.41   $98.40   $98.40  
  Purchase #4 $236.96   8.255%   $256.521   $256.52   $256.50   $256.50  
  Purchase #5 $11.34   11.252%   $12.616   $12.62   $12.60   $12.60  
  Purchase #6 $20.80   5.290%   $21.9003   $21.90   $21.90   $21.90  
  Purchase #7 $47.54   8.213%   $51.4445   $51.44   $51.45   $51.40  
  7 purchase totals = $859.89       $940.6578   $940.65   $940.60   $940.60