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 $114.53   6.826%   $122.3478   $122.35   $122.35   $122.30  
  Purchase #2 $249.72   9.346%   $273.0588   $273.06   $273.05   $273.10  
  Purchase #3 $223.66   5.315%   $235.5475   $235.55   $235.55   $235.50  
  Purchase #4 $235.33   9.687%   $258.1264   $258.13   $258.15   $258.10  
  Purchase #5 $196.73   3.778%   $204.1625   $204.16   $204.15   $204.20  
  Purchase #6 $88.25   5.158%   $92.8019   $92.80   $92.80   $92.80  
  Purchase #7 $235.33   6.133%   $249.7628   $249.76   $249.75   $249.80  
  7 purchase totals = $1,343.55       $1,435.8077   $1,435.81   $1,435.80   $1,435.80