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 $38.77   6.496%   $41.2885   $41.29   $41.30   $41.30  
  Purchase #2 $47.69   7.593%   $51.3111   $51.31   $51.30   $51.30  
  Purchase #3 $79.94   11.328%   $88.9956   $89.00   $89.00   $89.00  
  Purchase #4 $19.56   5.194%   $20.5759   $20.58   $20.60   $20.60  
  Purchase #5 $6.91   8.118%   $7.471   $7.47   $7.45   $7.50  
  Purchase #6 $237.55   12.387%   $266.9753   $266.98   $267.00   $267.00  
  Purchase #7 $66.37   4.267%   $69.202   $69.20   $69.20   $69.20  
  7 purchase totals = $496.79       $545.8194   $545.83   $545.85   $545.90