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 $87.76   8.127%   $94.8923   $94.89   $94.90   $94.90  
  Purchase #2 $168.73   9.801%   $185.2672   $185.27   $185.25   $185.30  
  Purchase #3 $148.84   3.203%   $153.6073   $153.61   $153.60   $153.60  
  Purchase #4 $113.62   5.628%   $120.0145   $120.01   $120.00   $120.00  
  Purchase #5 $25.57   5.127%   $26.881   $26.88   $26.90   $26.90  
  Purchase #6 $55.91   7.797%   $60.2693   $60.27   $60.25   $60.30  
  Purchase #7 $245.80   9.502%   $269.1559   $269.16   $269.15   $269.20  
  7 purchase totals = $846.23       $910.0875   $910.09   $910.05   $910.20