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 $13.51   3.614%   $13.9983   $14.00   $14.00   $14.00  
  Purchase #2 $98.33   6.423%   $104.6457   $104.65   $104.65   $104.60  
  Purchase #3 $116.92   12.311%   $131.314   $131.31   $131.30   $131.30  
  Purchase #4 $28.25   11.633%   $31.5363   $31.54   $31.55   $31.50  
  Purchase #5 $213.80   5.855%   $226.318   $226.32   $226.30   $226.30  
  Purchase #6 $129.26   3.296%   $133.5204   $133.52   $133.50   $133.50  
  Purchase #7 $103.76   11.423%   $115.6125   $115.61   $115.60   $115.60  
  7 purchase totals = $703.83       $756.9452   $756.95   $756.90   $756.80