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 $202.65   11.383%   $225.7176   $225.72   $225.70   $225.70  
  Purchase #2 $41.51   12.766%   $46.8092   $46.81   $46.80   $46.80  
  Purchase #3 $56.37   10.402%   $62.2336   $62.23   $62.25   $62.20  
  Purchase #4 $151.87   6.186%   $161.2647   $161.26   $161.25   $161.30  
  Purchase #5 $41.59   12.752%   $46.8936   $46.89   $46.90   $46.90  
  Purchase #6 $236.40   12.345%   $265.5836   $265.58   $265.60   $265.60  
  Purchase #7 $83.97   11.414%   $93.5543   $93.55   $93.55   $93.60  
  7 purchase totals = $814.36       $902.0566   $902.04   $902.05   $902.10