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 $247.84   7.603%   $266.6833   $266.68   $266.70   $266.70  
  Purchase #2 $24.30   11.747%   $27.1545   $27.15   $27.15   $27.20  
  Purchase #3 $244.93   11.688%   $273.5574   $273.56   $273.55   $273.60  
  Purchase #4 $92.26   3.829%   $95.7926   $95.79   $95.80   $95.80  
  Purchase #5 $233.35   10.679%   $258.2694   $258.27   $258.25   $258.30  
  Purchase #6 $237.30   5.532%   $250.4274   $250.43   $250.45   $250.40  
  Purchase #7 $160.32   7.276%   $171.9849   $171.98   $172.00   $172.00  
  7 purchase totals = $1,240.30       $1,343.8695   $1,343.86   $1,343.90   $1,344.00