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 $66.41   8.277%   $71.9068   $71.91   $71.90   $71.90  
  Purchase #2 $166.48   6.386%   $177.1114   $177.11   $177.10   $177.10  
  Purchase #3 $231.36   8.664%   $251.405   $251.41   $251.40   $251.40  
  Purchase #4 $18.57   3.848%   $19.2846   $19.28   $19.30   $19.30  
  Purchase #5 $129.34   12.140%   $145.0419   $145.04   $145.05   $145.00  
  Purchase #6 $28.87   5.314%   $30.4042   $30.40   $30.40   $30.40  
  Purchase #7 $183.30   11.776%   $204.8854   $204.89   $204.90   $204.90  
  7 purchase totals = $824.33       $900.0393   $900.04   $900.05   $900.00