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 $223.98   9.300%   $244.8101   $244.81   $244.80   $244.80  
  Purchase #2 $151.94   6.282%   $161.4849   $161.48   $161.50   $161.50  
  Purchase #3 $69.25   7.353%   $74.342   $74.34   $74.35   $74.30  
  Purchase #4 $60.99   3.793%   $63.3034   $63.30   $63.30   $63.30  
  Purchase #5 $157.78   6.443%   $167.9458   $167.95   $167.95   $167.90  
  Purchase #6 $237.74   12.364%   $267.1342   $267.13   $267.15   $267.10  
  Purchase #7 $60.90   8.803%   $66.261   $66.26   $66.25   $66.30  
  7 purchase totals = $962.58       $1,045.2814   $1,045.27   $1,045.30   $1,045.20