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 $6.78   4.389%   $7.0776   $7.08   $7.10   $7.10  
  Purchase #2 $172.56   10.529%   $190.7288   $190.73   $190.75   $190.70  
  Purchase #3 $172.54   6.288%   $183.3893   $183.39   $183.40   $183.40  
  Purchase #4 $230.31   6.183%   $244.5501   $244.55   $244.55   $244.60  
  Purchase #5 $101.27   11.285%   $112.6983   $112.70   $112.70   $112.70  
  Purchase #6 $211.88   10.616%   $234.3732   $234.37   $234.35   $234.40  
  Purchase #7 $104.53   8.817%   $113.7464   $113.75   $113.75   $113.70  
  7 purchase totals = $999.87       $1,086.5637   $1,086.57   $1,086.60   $1,086.60