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 $169.85   3.820%   $176.3383   $176.34   $176.35   $176.30  
  Purchase #2 $226.83   11.864%   $253.7411   $253.74   $253.75   $253.70  
  Purchase #3 $215.86   4.584%   $225.755   $225.76   $225.75   $225.80  
  Purchase #4 $162.37   11.779%   $181.4956   $181.50   $181.50   $181.50  
  Purchase #5 $144.61   4.650%   $151.3344   $151.33   $151.35   $151.30  
  Purchase #6 $29.44   10.317%   $32.4773   $32.48   $32.50   $32.50  
  Purchase #7 $245.97   6.411%   $261.7391   $261.74   $261.75   $261.70  
  7 purchase totals = $1,194.93       $1,282.8808   $1,282.89   $1,282.95   $1,282.80