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 $247.51   6.207%   $262.8729   $262.87   $262.85   $262.90  
  Purchase #2 $90.40   4.184%   $94.1823   $94.18   $94.20   $94.20  
  Purchase #3 $236.66   12.405%   $266.0177   $266.02   $266.00   $266.00  
  Purchase #4 $11.62   5.388%   $12.2461   $12.25   $12.25   $12.20  
  Purchase #5 $90.39   7.321%   $97.0075   $97.01   $97.00   $97.00  
  Purchase #6 $233.65   8.481%   $253.4659   $253.47   $253.45   $253.50  
  Purchase #7 $34.81   5.406%   $36.6918   $36.69   $36.70   $36.70  
  7 purchase totals = $945.04       $1,022.4842   $1,022.49   $1,022.45   $1,022.50