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 $226.69   6.482%   $241.384   $241.38   $241.40   $241.40  
  Purchase #2 $233.45   13.324%   $264.5549   $264.55   $264.55   $264.60  
  Purchase #3 $221.99   4.236%   $231.3935   $231.39   $231.40   $231.40  
  Purchase #4 $231.57   12.672%   $260.9146   $260.91   $260.90   $260.90  
  Purchase #5 $195.29   3.557%   $202.2365   $202.24   $202.25   $202.20  
  Purchase #6 $92.44   4.862%   $96.9344   $96.93   $96.95   $96.90  
  Purchase #7 $66.89   8.780%   $72.7629   $72.76   $72.75   $72.80  
  7 purchase totals = $1,268.32       $1,370.1808   $1,370.16   $1,370.20   $1,370.20