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 $10.90   7.821%   $11.7525   $11.75   $11.75   $11.80  
  Purchase #2 $18.66   7.135%   $19.9914   $19.99   $20.00   $20.00  
  Purchase #3 $137.55   5.544%   $145.1758   $145.18   $145.20   $145.20  
  Purchase #4 $70.53   3.598%   $73.0677   $73.07   $73.05   $73.10  
  Purchase #5 $99.50   5.630%   $105.1019   $105.10   $105.10   $105.10  
  Purchase #6 $46.81   7.445%   $50.295   $50.30   $50.30   $50.30  
  Purchase #7 $66.62   8.436%   $72.2401   $72.24   $72.25   $72.20  
  7 purchase totals = $450.57       $477.6244   $477.63   $477.65   $477.70