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 $210.95   9.863%   $231.756   $231.76   $231.75   $231.80  
  Purchase #2 $69.62   6.145%   $73.8981   $73.90   $73.90   $73.90  
  Purchase #3 $56.74   13.692%   $64.5088   $64.51   $64.50   $64.50  
  Purchase #4 $223.31   6.146%   $237.0346   $237.03   $237.05   $237.00  
  Purchase #5 $169.54   10.408%   $187.1857   $187.19   $187.20   $187.20  
  Purchase #6 $151.64   9.681%   $166.3203   $166.32   $166.30   $166.30  
  Purchase #7 $222.42   6.378%   $236.6059   $236.61   $236.60   $236.60  
  7 purchase totals = $1,104.22       $1,197.3094   $1,197.32   $1,197.30   $1,197.30