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 $191.66   4.848%   $200.9517   $200.95   $200.95   $201.00  
  Purchase #2 $60.95   10.697%   $67.4698   $67.47   $67.45   $67.50  
  Purchase #3 $168.38   3.236%   $173.8288   $173.83   $173.85   $173.80  
  Purchase #4 $211.64   8.197%   $228.9881   $228.99   $229.00   $229.00  
  Purchase #5 $183.86   6.349%   $195.5333   $195.53   $195.55   $195.50  
  Purchase #6 $199.54   10.690%   $220.8708   $220.87   $220.85   $220.90  
  Purchase #7 $209.47   10.716%   $231.9168   $231.92   $231.90   $231.90  
  7 purchase totals = $1,225.50       $1,319.5593   $1,319.56   $1,319.55   $1,319.60