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 $48.76   6.227%   $51.7963   $51.80   $51.80   $51.80  
  Purchase #2 $192.95   10.209%   $212.6483   $212.65   $212.65   $212.60  
  Purchase #3 $165.59   7.583%   $178.1467   $178.15   $178.15   $178.10  
  Purchase #4 $182.32   6.218%   $193.6567   $193.66   $193.65   $193.70  
  Purchase #5 $105.55   7.225%   $113.176   $113.18   $113.20   $113.20  
  Purchase #6 $194.39   3.697%   $201.5766   $201.58   $201.60   $201.60  
  Purchase #7 $14.34   9.392%   $15.6868   $15.69   $15.70   $15.70  
  7 purchase totals = $903.90       $966.6874   $966.71   $966.75   $966.70