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 $208.69   12.380%   $234.5258   $234.53   $234.55   $234.50  
  Purchase #2 $6.41   10.188%   $7.0631   $7.06   $7.05   $7.10  
  Purchase #3 $12.77   4.161%   $13.3014   $13.30   $13.30   $13.30  
  Purchase #4 $99.96   5.666%   $105.6237   $105.62   $105.60   $105.60  
  Purchase #5 $165.92   6.315%   $176.3978   $176.40   $176.40   $176.40  
  Purchase #6 $93.63   4.320%   $97.6748   $97.67   $97.65   $97.70  
  Purchase #7 $181.28   10.432%   $200.1911   $200.19   $200.20   $200.20  
  7 purchase totals = $768.66       $834.7777   $834.77   $834.75   $834.80