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 $104.89   10.397%   $115.7954   $115.80   $115.80   $115.80  
  Purchase #2 $92.84   4.187%   $96.7272   $96.73   $96.75   $96.70  
  Purchase #3 $55.42   4.631%   $57.9865   $57.99   $58.00   $58.00  
  Purchase #4 $182.62   13.725%   $207.6846   $207.68   $207.70   $207.70  
  Purchase #5 $15.44   3.764%   $16.0212   $16.02   $16.00   $16.00  
  Purchase #6 $165.89   3.725%   $172.0694   $172.07   $172.05   $172.10  
  Purchase #7 $59.57   3.113%   $61.4244   $61.42   $61.40   $61.40  
  7 purchase totals = $676.67       $727.7087   $727.71   $727.70   $727.70