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 $113.99   4.721%   $119.3715   $119.37   $119.35   $119.40  
  Purchase #2 $105.97   10.460%   $117.0545   $117.05   $117.05   $117.10  
  Purchase #3 $87.81   13.147%   $99.3544   $99.35   $99.35   $99.40  
  Purchase #4 $241.27   8.448%   $261.6525   $261.65   $261.65   $261.70  
  Purchase #5 $147.59   5.821%   $156.1812   $156.18   $156.20   $156.20  
  Purchase #6 $74.96   12.313%   $84.1898   $84.19   $84.20   $84.20  
  Purchase #7 $192.43   13.615%   $218.6293   $218.63   $218.65   $218.60  
  7 purchase totals = $964.02       $1,056.4332   $1,056.42   $1,056.45   $1,056.60