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 $87.63   8.262%   $94.87   $94.87   $94.85   $94.90  
  Purchase #2 $62.42   11.258%   $69.4472   $69.45   $69.45   $69.40  
  Purchase #3 $113.88   8.629%   $123.7067   $123.71   $123.70   $123.70  
  Purchase #4 $71.26   4.179%   $74.238   $74.24   $74.25   $74.20  
  Purchase #5 $54.26   8.184%   $58.7006   $58.70   $58.70   $58.70  
  Purchase #6 $117.90   4.689%   $123.4283   $123.43   $123.45   $123.40  
  Purchase #7 $63.83   10.272%   $70.3866   $70.39   $70.40   $70.40  
  7 purchase totals = $571.18       $614.7774   $614.79   $614.80   $614.70