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 $59.41   13.326%   $67.327   $67.33   $67.35   $67.30  
  Purchase #2 $202.75   9.108%   $221.2165   $221.22   $221.20   $221.20  
  Purchase #3 $227.44   9.294%   $248.5783   $248.58   $248.60   $248.60  
  Purchase #4 $32.85   4.542%   $34.342   $34.34   $34.35   $34.30  
  Purchase #5 $203.69   5.708%   $215.3166   $215.32   $215.30   $215.30  
  Purchase #6 $182.37   9.433%   $199.573   $199.57   $199.55   $199.60  
  Purchase #7 $83.55   5.561%   $88.1962   $88.20   $88.20   $88.20  
  7 purchase totals = $992.06       $1,074.5496   $1,074.56   $1,074.55   $1,074.50