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 $178.71   7.251%   $191.6683   $191.67   $191.65   $191.70  
  Purchase #2 $55.98   13.616%   $63.6022   $63.60   $63.60   $63.60  
  Purchase #3 $6.47   6.751%   $6.9068   $6.91   $6.90   $6.90  
  Purchase #4 $98.50   5.637%   $104.0524   $104.05   $104.05   $104.10  
  Purchase #5 $209.31   4.110%   $217.9126   $217.91   $217.90   $217.90  
  Purchase #6 $175.69   5.137%   $184.7152   $184.72   $184.70   $184.70  
  Purchase #7 $51.66   4.670%   $54.0725   $54.07   $54.05   $54.10  
  7 purchase totals = $776.32       $822.9300   $822.93   $822.85   $823.00