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 $186.98   11.150%   $207.8283   $207.83   $207.85   $207.80  
  Purchase #2 $247.48   6.191%   $262.8015   $262.80   $262.80   $262.80  
  Purchase #3 $160.83   4.549%   $168.1462   $168.15   $168.15   $168.10  
  Purchase #4 $153.40   11.589%   $171.1775   $171.18   $171.20   $171.20  
  Purchase #5 $72.66   5.849%   $76.9099   $76.91   $76.90   $76.90  
  Purchase #6 $150.31   9.362%   $164.382   $164.38   $164.40   $164.40  
  Purchase #7 $200.69   12.840%   $226.4586   $226.46   $226.45   $226.50  
  7 purchase totals = $1,172.35       $1,277.7040   $1,277.71   $1,277.75   $1,277.70