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 $230.98   13.277%   $261.6472   $261.65   $261.65   $261.60  
  Purchase #2 $44.61   10.474%   $49.2825   $49.28   $49.30   $49.30  
  Purchase #3 $32.60   6.508%   $34.7216   $34.72   $34.70   $34.70  
  Purchase #4 $147.84   7.818%   $159.3981   $159.40   $159.40   $159.40  
  Purchase #5 $230.37   4.758%   $241.331   $241.33   $241.35   $241.30  
  Purchase #6 $61.79   8.757%   $67.201   $67.20   $67.20   $67.20  
  Purchase #7 $228.49   5.555%   $241.1826   $241.18   $241.20   $241.20  
  7 purchase totals = $976.68       $1,054.7640   $1,054.76   $1,054.80   $1,054.70