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 $38.50   8.267%   $41.6828   $41.68   $41.70   $41.70  
  Purchase #2 $165.73   4.606%   $173.3635   $173.36   $173.35   $173.40  
  Purchase #3 $240.88   11.575%   $268.7619   $268.76   $268.75   $268.80  
  Purchase #4 $100.91   7.182%   $108.1574   $108.16   $108.15   $108.20  
  Purchase #5 $227.53   10.573%   $251.5867   $251.59   $251.60   $251.60  
  Purchase #6 $63.42   4.548%   $66.3043   $66.30   $66.30   $66.30  
  Purchase #7 $239.92   9.104%   $261.7623   $261.76   $261.75   $261.80  
  7 purchase totals = $1,076.89       $1,171.6189   $1,171.61   $1,171.60   $1,171.80