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 $54.36   11.721%   $60.7315   $60.73   $60.75   $60.70  
  Purchase #2 $237.31   12.467%   $266.8954   $266.90   $266.90   $266.90  
  Purchase #3 $72.43   10.129%   $79.7664   $79.77   $79.75   $79.80  
  Purchase #4 $108.99   5.777%   $115.2864   $115.29   $115.30   $115.30  
  Purchase #5 $93.36   12.263%   $104.8087   $104.81   $104.80   $104.80  
  Purchase #6 $172.49   5.666%   $182.2633   $182.26   $182.25   $182.30  
  Purchase #7 $70.56   9.353%   $77.1595   $77.16   $77.15   $77.20  
  7 purchase totals = $809.50       $886.9112   $886.92   $886.90   $887.00