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 $62.42   11.381%   $69.524   $69.52   $69.50   $69.50  
  Purchase #2 $73.90   3.109%   $76.1976   $76.20   $76.20   $76.20  
  Purchase #3 $41.46   7.386%   $44.5222   $44.52   $44.50   $44.50  
  Purchase #4 $204.69   11.636%   $228.5077   $228.51   $228.50   $228.50  
  Purchase #5 $52.69   10.639%   $58.2957   $58.30   $58.30   $58.30  
  Purchase #6 $56.73   13.747%   $64.5287   $64.53   $64.55   $64.50  
  Purchase #7 $172.40   3.366%   $178.203   $178.20   $178.20   $178.20  
  7 purchase totals = $664.29       $719.7789   $719.78   $719.75   $719.70