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 $196.41   13.654%   $223.2278   $223.23   $223.25   $223.20  
  Purchase #2 $118.92   12.423%   $133.6934   $133.69   $133.70   $133.70  
  Purchase #3 $132.96   5.842%   $140.7275   $140.73   $140.75   $140.70  
  Purchase #4 $200.51   5.615%   $211.7686   $211.77   $211.75   $211.80  
  Purchase #5 $125.62   9.298%   $137.3001   $137.30   $137.30   $137.30  
  Purchase #6 $236.61   3.668%   $245.2889   $245.29   $245.30   $245.30  
  Purchase #7 $32.59   6.690%   $34.7703   $34.77   $34.75   $34.80  
  7 purchase totals = $1,043.62       $1,126.7766   $1,126.78   $1,126.80   $1,126.80