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 $202.47   11.118%   $224.9806   $224.98   $225.00   $225.00  
  Purchase #2 $226.55   4.257%   $236.1942   $236.19   $236.20   $236.20  
  Purchase #3 $118.36   13.146%   $133.9196   $133.92   $133.90   $133.90  
  Purchase #4 $247.54   12.797%   $279.2177   $279.22   $279.20   $279.20  
  Purchase #5 $122.99   4.405%   $128.4077   $128.41   $128.40   $128.40  
  Purchase #6 $237.58   3.164%   $245.097   $245.10   $245.10   $245.10  
  Purchase #7 $152.41   8.328%   $165.1027   $165.10   $165.10   $165.10  
  7 purchase totals = $1,307.90       $1,412.9195   $1,412.92   $1,412.90   $1,412.90