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 $41.49   10.873%   $46.0012   $46.00   $46.00   $46.00  
  Purchase #2 $223.26   7.392%   $239.7634   $239.76   $239.75   $239.80  
  Purchase #3 $50.64   5.385%   $53.367   $53.37   $53.35   $53.40  
  Purchase #4 $186.91   10.337%   $206.2309   $206.23   $206.25   $206.20  
  Purchase #5 $120.63   4.229%   $125.7314   $125.73   $125.75   $125.70  
  Purchase #6 $45.89   7.320%   $49.2491   $49.25   $49.25   $49.20  
  Purchase #7 $79.33   6.672%   $84.6229   $84.62   $84.60   $84.60  
  7 purchase totals = $748.15       $804.9659   $804.96   $804.95   $804.90