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 $150.50   12.168%   $168.8128   $168.81   $168.80   $168.80  
  Purchase #2 $77.40   13.541%   $87.8807   $87.88   $87.90   $87.90  
  Purchase #3 $175.85   6.744%   $187.7093   $187.71   $187.70   $187.70  
  Purchase #4 $89.30   9.509%   $97.7915   $97.79   $97.80   $97.80  
  Purchase #5 $87.85   10.628%   $97.1867   $97.19   $97.20   $97.20  
  Purchase #6 $50.95   7.250%   $54.6439   $54.64   $54.65   $54.60  
  Purchase #7 $167.38   12.391%   $188.1201   $188.12   $188.10   $188.10  
  7 purchase totals = $799.23       $882.1450   $882.14   $882.15   $882.10