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 $32.49   5.409%   $34.2474   $34.25   $34.25   $34.20  
  Purchase #2 $184.29   12.291%   $206.9411   $206.94   $206.95   $206.90  
  Purchase #3 $146.75   6.137%   $155.756   $155.76   $155.75   $155.80  
  Purchase #4 $216.85   7.285%   $232.6475   $232.65   $232.65   $232.60  
  Purchase #5 $205.55   13.691%   $233.6919   $233.69   $233.70   $233.70  
  Purchase #6 $97.26   12.385%   $109.3057   $109.31   $109.30   $109.30  
  Purchase #7 $104.71   12.140%   $117.4218   $117.42   $117.40   $117.40  
  7 purchase totals = $987.90       $1,090.0114   $1,090.02   $1,090.00   $1,089.90