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 $245.65   11.756%   $274.5286   $274.53   $274.55   $274.50  
  Purchase #2 $233.54   7.483%   $251.0158   $251.02   $251.00   $251.00  
  Purchase #3 $184.97   13.857%   $210.6013   $210.60   $210.60   $210.60  
  Purchase #4 $60.82   10.182%   $67.0127   $67.01   $67.00   $67.00  
  Purchase #5 $189.70   11.757%   $212.003   $212.00   $212.00   $212.00  
  Purchase #6 $49.50   7.444%   $53.1848   $53.18   $53.20   $53.20  
  Purchase #7 $103.33   10.719%   $114.4059   $114.41   $114.40   $114.40  
  7 purchase totals = $1,067.51       $1,182.7521   $1,182.75   $1,182.75   $1,182.70