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 $43.49   7.699%   $46.8383   $46.84   $46.85   $46.80  
  Purchase #2 $197.53   13.339%   $223.8785   $223.88   $223.90   $223.90  
  Purchase #3 $66.78   9.262%   $72.9652   $72.97   $72.95   $73.00  
  Purchase #4 $107.63   5.700%   $113.7649   $113.76   $113.75   $113.80  
  Purchase #5 $95.94   9.122%   $104.6916   $104.69   $104.70   $104.70  
  Purchase #6 $94.76   13.299%   $107.3621   $107.36   $107.35   $107.40  
  Purchase #7 $71.32   5.115%   $74.968   $74.97   $74.95   $75.00  
  7 purchase totals = $677.45       $744.4686   $744.47   $744.45   $744.60