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 $250.29   10.370%   $276.2451   $276.25   $276.25   $276.20  
  Purchase #2 $145.44   4.766%   $152.3717   $152.37   $152.35   $152.40  
  Purchase #3 $227.98   9.457%   $249.5401   $249.54   $249.55   $249.50  
  Purchase #4 $78.61   3.675%   $81.4989   $81.50   $81.50   $81.50  
  Purchase #5 $187.35   7.700%   $201.776   $201.78   $201.80   $201.80  
  Purchase #6 $142.85   3.790%   $148.264   $148.26   $148.25   $148.30  
  Purchase #7 $21.85   4.322%   $22.7944   $22.79   $22.80   $22.80  
  7 purchase totals = $1,054.37       $1,132.4902   $1,132.49   $1,132.50   $1,132.50