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 $62.78   11.120%   $69.7611   $69.76   $69.75   $69.80  
  Purchase #2 $234.64   7.742%   $252.8058   $252.81   $252.80   $252.80  
  Purchase #3 $178.50   9.180%   $194.8863   $194.89   $194.90   $194.90  
  Purchase #4 $122.30   9.464%   $133.8745   $133.87   $133.85   $133.90  
  Purchase #5 $49.98   6.721%   $53.3392   $53.34   $53.35   $53.30  
  Purchase #6 $132.46   5.300%   $139.4804   $139.48   $139.50   $139.50  
  Purchase #7 $150.30   6.772%   $160.4783   $160.48   $160.50   $160.50  
  7 purchase totals = $930.96       $1,004.6256   $1,004.63   $1,004.65   $1,004.70