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 $55.99   5.539%   $59.0913   $59.09   $59.10   $59.10  
  Purchase #2 $205.60   5.712%   $217.3439   $217.34   $217.35   $217.30  
  Purchase #3 $5.98   11.427%   $6.6633   $6.66   $6.65   $6.70  
  Purchase #4 $101.30   7.221%   $108.6149   $108.61   $108.60   $108.60  
  Purchase #5 $163.37   7.410%   $175.4757   $175.48   $175.50   $175.50  
  Purchase #6 $151.86   6.141%   $161.1857   $161.19   $161.20   $161.20  
  Purchase #7 $15.73   6.593%   $16.7671   $16.77   $16.75   $16.80  
  7 purchase totals = $699.83       $745.1419   $745.14   $745.15   $745.20