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 $34.87   5.373%   $36.7436   $36.74   $36.75   $36.70  
  Purchase #2 $16.49   4.778%   $17.2779   $17.28   $17.30   $17.30  
  Purchase #3 $117.90   4.856%   $123.6252   $123.63   $123.65   $123.60  
  Purchase #4 $197.61   10.226%   $217.8176   $217.82   $217.80   $217.80  
  Purchase #5 $145.82   12.487%   $164.0285   $164.03   $164.05   $164.00  
  Purchase #6 $203.85   11.571%   $227.4375   $227.44   $227.45   $227.40  
  Purchase #7 $75.40   11.359%   $83.9647   $83.96   $83.95   $84.00  
  7 purchase totals = $791.94       $870.8950   $870.90   $870.95   $870.80