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 $170.85   12.381%   $192.0029   $192.00   $192.00   $192.00  
  Purchase #2 $72.89   4.453%   $76.1358   $76.14   $76.15   $76.10  
  Purchase #3 $62.59   10.495%   $69.1588   $69.16   $69.15   $69.20  
  Purchase #4 $49.42   7.868%   $53.3084   $53.31   $53.30   $53.30  
  Purchase #5 $189.73   3.413%   $196.2055   $196.21   $196.20   $196.20  
  Purchase #6 $86.49   10.562%   $95.6251   $95.63   $95.65   $95.60  
  Purchase #7 $246.50   11.181%   $274.0612   $274.06   $274.05   $274.10  
  7 purchase totals = $878.47       $956.4977   $956.51   $956.50   $956.50