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 $122.83   9.248%   $134.1893   $134.19   $134.20   $134.20  
  Purchase #2 $240.95   5.836%   $255.0118   $255.01   $255.00   $255.00  
  Purchase #3 $86.56   12.345%   $97.2458   $97.25   $97.25   $97.20  
  Purchase #4 $231.80   4.787%   $242.8963   $242.90   $242.90   $242.90  
  Purchase #5 $121.55   7.299%   $130.4219   $130.42   $130.40   $130.40  
  Purchase #6 $163.95   13.346%   $185.8308   $185.83   $185.85   $185.80  
  Purchase #7 $10.26   8.717%   $11.1544   $11.15   $11.15   $11.20  
  7 purchase totals = $977.90       $1,056.7503   $1,056.75   $1,056.75   $1,056.70