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 $189.47   10.202%   $208.7997   $208.80   $208.80   $208.80  
  Purchase #2 $94.84   3.135%   $97.8132   $97.81   $97.80   $97.80  
  Purchase #3 $129.72   8.663%   $140.9576   $140.96   $140.95   $141.00  
  Purchase #4 $78.40   10.647%   $86.7472   $86.75   $86.75   $86.70  
  Purchase #5 $37.90   9.790%   $41.6104   $41.61   $41.60   $41.60  
  Purchase #6 $167.62   11.390%   $186.7119   $186.71   $186.70   $186.70  
  Purchase #7 $83.88   8.522%   $91.0283   $91.03   $91.05   $91.00  
  7 purchase totals = $781.83       $853.6683   $853.67   $853.65   $853.60