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 $235.78   3.848%   $244.8528   $244.85   $244.85   $244.90  
  Purchase #2 $185.97   10.533%   $205.5582   $205.56   $205.55   $205.60  
  Purchase #3 $140.36   9.732%   $154.0198   $154.02   $154.00   $154.00  
  Purchase #4 $178.67   4.370%   $186.4779   $186.48   $186.50   $186.50  
  Purchase #5 $33.65   5.489%   $35.497   $35.50   $35.50   $35.50  
  Purchase #6 $62.63   8.366%   $67.8696   $67.87   $67.85   $67.90  
  Purchase #7 $120.25   10.211%   $132.5287   $132.53   $132.55   $132.50  
  7 purchase totals = $957.31       $1,026.8040   $1,026.81   $1,026.80   $1,026.90