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 $214.67   9.453%   $234.9628   $234.96   $234.95   $235.00  
  Purchase #2 $181.90   5.111%   $191.1969   $191.20   $191.20   $191.20  
  Purchase #3 $42.34   13.134%   $47.9009   $47.90   $47.90   $47.90  
  Purchase #4 $105.29   5.174%   $110.7377   $110.74   $110.75   $110.70  
  Purchase #5 $24.32   10.724%   $26.9281   $26.93   $26.95   $26.90  
  Purchase #6 $155.42   4.762%   $162.8211   $162.82   $162.80   $162.80  
  Purchase #7 $99.62   4.828%   $104.4297   $104.43   $104.45   $104.40  
  7 purchase totals = $823.56       $878.9772   $878.98   $879.00   $878.90