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 $245.75   6.548%   $261.8417   $261.84   $261.85   $261.80  
  Purchase #2 $219.53   10.555%   $242.7014   $242.70   $242.70   $242.70  
  Purchase #3 $181.96   11.327%   $202.5706   $202.57   $202.55   $202.60  
  Purchase #4 $121.40   13.861%   $138.2273   $138.23   $138.25   $138.20  
  Purchase #5 $152.76   11.457%   $170.2617   $170.26   $170.25   $170.30  
  Purchase #6 $92.39   4.694%   $96.7268   $96.73   $96.75   $96.70  
  Purchase #7 $178.77   6.185%   $189.8269   $189.83   $189.85   $189.80  
  7 purchase totals = $1,192.56       $1,302.1564   $1,302.16   $1,302.20   $1,302.10