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 $48.63   10.504%   $53.7381   $53.74   $53.75   $53.70  
  Purchase #2 $116.41   6.594%   $124.0861   $124.09   $124.10   $124.10  
  Purchase #3 $199.87   9.682%   $219.2214   $219.22   $219.20   $219.20  
  Purchase #4 $223.70   11.624%   $249.7029   $249.70   $249.70   $249.70  
  Purchase #5 $77.36   5.295%   $81.4562   $81.46   $81.45   $81.50  
  Purchase #6 $232.61   7.117%   $249.1649   $249.16   $249.15   $249.20  
  Purchase #7 $44.58   7.153%   $47.7688   $47.77   $47.75   $47.80  
  7 purchase totals = $943.16       $1,025.1384   $1,025.14   $1,025.10   $1,025.20