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 $113.59   5.476%   $119.8102   $119.81   $119.80   $119.80  
  Purchase #2 $193.90   11.220%   $215.6556   $215.66   $215.65   $215.70  
  Purchase #3 $240.56   11.535%   $268.3086   $268.31   $268.30   $268.30  
  Purchase #4 $88.27   11.476%   $98.3999   $98.40   $98.40   $98.40  
  Purchase #5 $85.90   10.652%   $95.0501   $95.05   $95.05   $95.10  
  Purchase #6 $173.85   9.722%   $190.7517   $190.75   $190.75   $190.80  
  Purchase #7 $6.50   13.257%   $7.3617   $7.36   $7.35   $7.40  
  7 purchase totals = $902.57       $995.3378   $995.34   $995.30   $995.50