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 $64.91   13.646%   $73.7676   $73.77   $73.75   $73.80  
  Purchase #2 $52.42   4.194%   $54.6185   $54.62   $54.60   $54.60  
  Purchase #3 $181.99   10.420%   $200.9534   $200.95   $200.95   $201.00  
  Purchase #4 $186.87   8.484%   $202.7241   $202.72   $202.70   $202.70  
  Purchase #5 $72.47   9.303%   $79.2119   $79.21   $79.20   $79.20  
  Purchase #6 $81.82   4.658%   $85.6312   $85.63   $85.65   $85.60  
  Purchase #7 $238.31   11.799%   $266.4282   $266.43   $266.45   $266.40  
  7 purchase totals = $878.79       $963.3349   $963.33   $963.30   $963.30