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 $190.94   4.770%   $200.0478   $200.05   $200.05   $200.00  
  Purchase #2 $43.58   5.337%   $45.9059   $45.91   $45.90   $45.90  
  Purchase #3 $92.44   5.724%   $97.7313   $97.73   $97.75   $97.70  
  Purchase #4 $16.32   6.202%   $17.3322   $17.33   $17.35   $17.30  
  Purchase #5 $171.68   13.630%   $195.08   $195.08   $195.10   $195.10  
  Purchase #6 $242.30   12.372%   $272.2774   $272.28   $272.30   $272.30  
  Purchase #7 $112.33   10.434%   $124.0505   $124.05   $124.05   $124.10  
  7 purchase totals = $869.59       $952.4251   $952.43   $952.50   $952.40