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 $17.28   6.857%   $18.4649   $18.46   $18.45   $18.50  
  Purchase #2 $105.55   4.207%   $109.9905   $109.99   $110.00   $110.00  
  Purchase #3 $53.84   4.719%   $56.3807   $56.38   $56.40   $56.40  
  Purchase #4 $244.74   11.821%   $273.6707   $273.67   $273.65   $273.70  
  Purchase #5 $170.44   7.442%   $183.1241   $183.12   $183.10   $183.10  
  Purchase #6 $109.35   11.749%   $122.1975   $122.20   $122.20   $122.20  
  Purchase #7 $30.57   6.470%   $32.5479   $32.55   $32.55   $32.50  
  7 purchase totals = $731.77       $796.3763   $796.37   $796.35   $796.40