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 $164.88   12.548%   $185.5691   $185.57   $185.55   $185.60  
  Purchase #2 $234.48   8.166%   $253.6276   $253.63   $253.65   $253.60  
  Purchase #3 $39.97   9.132%   $43.6201   $43.62   $43.60   $43.60  
  Purchase #4 $206.69   9.697%   $226.7327   $226.73   $226.75   $226.70  
  Purchase #5 $27.43   7.192%   $29.4028   $29.40   $29.40   $29.40  
  Purchase #6 $82.30   5.511%   $86.8356   $86.84   $86.85   $86.80  
  Purchase #7 $226.70   4.302%   $236.4526   $236.45   $236.45   $236.50  
  7 purchase totals = $982.45       $1,062.2405   $1,062.24   $1,062.25   $1,062.20