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 $59.97   6.798%   $64.0468   $64.05   $64.05   $64.00  
  Purchase #2 $117.80   4.306%   $122.8725   $122.87   $122.85   $122.90  
  Purchase #3 $32.26   5.709%   $34.1017   $34.10   $34.10   $34.10  
  Purchase #4 $163.32   12.695%   $184.0535   $184.05   $184.05   $184.10  
  Purchase #5 $38.54   7.522%   $41.439   $41.44   $41.45   $41.40  
  Purchase #6 $109.65   6.834%   $117.1435   $117.14   $117.15   $117.10  
  Purchase #7 $201.62   4.766%   $211.2292   $211.23   $211.25   $211.20  
  7 purchase totals = $723.16       $774.8862   $774.88   $774.90   $774.80