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 $216.81   11.233%   $241.1643   $241.16   $241.15   $241.20  
  Purchase #2 $132.67   6.206%   $140.9035   $140.90   $140.90   $140.90  
  Purchase #3 $128.38   10.862%   $142.3246   $142.32   $142.30   $142.30  
  Purchase #4 $193.48   4.501%   $202.1885   $202.19   $202.20   $202.20  
  Purchase #5 $209.31   10.387%   $231.051   $231.05   $231.05   $231.10  
  Purchase #6 $190.60   13.521%   $216.371   $216.37   $216.35   $216.40  
  Purchase #7 $226.85   11.802%   $253.6228   $253.62   $253.60   $253.60  
  7 purchase totals = $1,298.10       $1,427.6257   $1,427.61   $1,427.55   $1,427.70