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 $45.76   13.307%   $51.8493   $51.85   $51.85   $51.80  
  Purchase #2 $237.52   13.762%   $270.2075   $270.21   $270.20   $270.20  
  Purchase #3 $168.62   8.351%   $182.7015   $182.70   $182.70   $182.70  
  Purchase #4 $52.32   9.231%   $57.1497   $57.15   $57.15   $57.10  
  Purchase #5 $162.72   3.190%   $167.9108   $167.91   $167.90   $167.90  
  Purchase #6 $140.43   6.795%   $149.9722   $149.97   $149.95   $150.00  
  Purchase #7 $168.44   4.137%   $175.4084   $175.41   $175.40   $175.40  
  7 purchase totals = $975.81       $1,055.1994   $1,055.20   $1,055.15   $1,055.10