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 $49.42   4.776%   $51.7803   $51.78   $51.80   $51.80  
  Purchase #2 $83.84   13.503%   $95.1609   $95.16   $95.15   $95.20  
  Purchase #3 $105.36   8.807%   $114.6391   $114.64   $114.65   $114.60  
  Purchase #4 $180.50   8.492%   $195.8281   $195.83   $195.85   $195.80  
  Purchase #5 $124.46   9.546%   $136.341   $136.34   $136.35   $136.30  
  Purchase #6 $57.49   13.831%   $65.4414   $65.44   $65.45   $65.40  
  Purchase #7 $15.93   11.413%   $17.7481   $17.75   $17.75   $17.70  
  7 purchase totals = $617.00       $676.9389   $676.94   $677.00   $676.80