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 $203.25   4.584%   $212.567   $212.57   $212.55   $212.60  
  Purchase #2 $114.78   9.698%   $125.9114   $125.91   $125.90   $125.90  
  Purchase #3 $248.58   11.564%   $277.3258   $277.33   $277.35   $277.30  
  Purchase #4 $216.40   13.746%   $246.1463   $246.15   $246.15   $246.10  
  Purchase #5 $101.95   12.620%   $114.8161   $114.82   $114.80   $114.80  
  Purchase #6 $249.95   9.460%   $273.5953   $273.60   $273.60   $273.60  
  Purchase #7 $131.51   11.441%   $146.5561   $146.56   $146.55   $146.60  
  7 purchase totals = $1,266.42       $1,396.9180   $1,396.94   $1,396.90   $1,396.90