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 $226.94   11.703%   $253.4988   $253.50   $253.50   $253.50  
  Purchase #2 $247.86   6.762%   $264.6203   $264.62   $264.60   $264.60  
  Purchase #3 $74.32   9.177%   $81.1403   $81.14   $81.15   $81.10  
  Purchase #4 $167.90   13.537%   $190.6286   $190.63   $190.65   $190.60  
  Purchase #5 $14.88   12.804%   $16.7852   $16.79   $16.80   $16.80  
  Purchase #6 $220.81   13.516%   $250.6547   $250.65   $250.65   $250.70  
  Purchase #7 $41.97   12.606%   $47.2607   $47.26   $47.25   $47.30  
  7 purchase totals = $994.68       $1,104.5886   $1,104.59   $1,104.60   $1,104.60