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 $197.59   4.672%   $206.8214   $206.82   $206.80   $206.80  
  Purchase #2 $124.29   13.759%   $141.3911   $141.39   $141.40   $141.40  
  Purchase #3 $166.56   3.372%   $172.1764   $172.18   $172.20   $172.20  
  Purchase #4 $198.34   4.131%   $206.5334   $206.53   $206.55   $206.50  
  Purchase #5 $202.95   5.619%   $214.3538   $214.35   $214.35   $214.40  
  Purchase #6 $241.83   10.803%   $267.9549   $267.95   $267.95   $268.00  
  Purchase #7 $128.56   10.745%   $142.3738   $142.37   $142.35   $142.40  
  7 purchase totals = $1,260.12       $1,351.6048   $1,351.59   $1,351.60   $1,351.70