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 $230.67   11.288%   $256.708   $256.71   $256.70   $256.70  
  Purchase #2 $225.47   13.223%   $255.2839   $255.28   $255.30   $255.30  
  Purchase #3 $95.93   13.551%   $108.9295   $108.93   $108.95   $108.90  
  Purchase #4 $175.36   7.454%   $188.4313   $188.43   $188.45   $188.40  
  Purchase #5 $220.70   9.377%   $241.395   $241.40   $241.40   $241.40  
  Purchase #6 $85.57   11.650%   $95.5389   $95.54   $95.55   $95.50  
  Purchase #7 $52.67   8.787%   $57.2981   $57.30   $57.30   $57.30  
  7 purchase totals = $1,086.37       $1,203.5847   $1,203.59   $1,203.65   $1,203.50