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 $224.73   3.670%   $232.9776   $232.98   $233.00   $233.00  
  Purchase #2 $248.44   6.515%   $264.6259   $264.63   $264.65   $264.60  
  Purchase #3 $21.58   11.362%   $24.0319   $24.03   $24.05   $24.00  
  Purchase #4 $245.91   7.640%   $264.6975   $264.70   $264.70   $264.70  
  Purchase #5 $208.65   13.278%   $236.3545   $236.35   $236.35   $236.40  
  Purchase #6 $195.73   9.110%   $213.561   $213.56   $213.55   $213.60  
  Purchase #7 $169.34   9.683%   $185.7372   $185.74   $185.75   $185.70  
  7 purchase totals = $1,314.38       $1,421.9856   $1,421.99   $1,422.05   $1,422.00