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 $250.93   8.655%   $272.648   $272.65   $272.65   $272.60  
  Purchase #2 $205.80   6.871%   $219.9405   $219.94   $219.95   $219.90  
  Purchase #3 $30.73   6.394%   $32.6949   $32.69   $32.70   $32.70  
  Purchase #4 $184.43   6.197%   $195.8591   $195.86   $195.85   $195.90  
  Purchase #5 $184.72   9.103%   $201.5351   $201.54   $201.55   $201.50  
  Purchase #6 $78.42   12.239%   $88.0178   $88.02   $88.00   $88.00  
  Purchase #7 $248.66   3.653%   $257.7435   $257.74   $257.75   $257.70  
  7 purchase totals = $1,183.69       $1,268.4389   $1,268.44   $1,268.45   $1,268.30