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 $63.36   8.182%   $68.5441   $68.54   $68.55   $68.50  
  Purchase #2 $98.99   5.376%   $104.3117   $104.31   $104.30   $104.30  
  Purchase #3 $186.48   8.332%   $202.0175   $202.02   $202.00   $202.00  
  Purchase #4 $8.30   8.756%   $9.0267   $9.03   $9.05   $9.00  
  Purchase #5 $171.29   3.154%   $176.6925   $176.69   $176.70   $176.70  
  Purchase #6 $151.64   11.521%   $169.1104   $169.11   $169.10   $169.10  
  Purchase #7 $6.99   11.788%   $7.814   $7.81   $7.80   $7.80  
  7 purchase totals = $687.05       $737.5169   $737.51   $737.50   $737.40