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 $207.73   13.443%   $235.6551   $235.66   $235.65   $235.70  
  Purchase #2 $206.87   4.335%   $215.8378   $215.84   $215.85   $215.80  
  Purchase #3 $126.61   5.288%   $133.3051   $133.31   $133.30   $133.30  
  Purchase #4 $128.92   11.872%   $144.2254   $144.23   $144.25   $144.20  
  Purchase #5 $52.73   9.553%   $57.7673   $57.77   $57.75   $57.80  
  Purchase #6 $135.49   13.657%   $153.9939   $153.99   $154.00   $154.00  
  Purchase #7 $234.38   12.125%   $262.7986   $262.80   $262.80   $262.80  
  7 purchase totals = $1,092.73       $1,203.5832   $1,203.60   $1,203.60   $1,203.60