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 $58.58   6.832%   $62.5822   $62.58   $62.60   $62.60  
  Purchase #2 $199.93   6.577%   $213.0794   $213.08   $213.10   $213.10  
  Purchase #3 $14.31   6.608%   $15.2556   $15.26   $15.25   $15.30  
  Purchase #4 $149.64   13.347%   $169.6125   $169.61   $169.60   $169.60  
  Purchase #5 $59.31   5.126%   $62.3502   $62.35   $62.35   $62.40  
  Purchase #6 $238.94   6.643%   $254.8128   $254.81   $254.80   $254.80  
  Purchase #7 $164.25   10.642%   $181.7295   $181.73   $181.75   $181.70  
  7 purchase totals = $884.96       $959.4222   $959.42   $959.45   $959.50