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 $201.39   8.487%   $218.482   $218.48   $218.50   $218.50  
  Purchase #2 $128.53   4.690%   $134.5581   $134.56   $134.55   $134.60  
  Purchase #3 $53.42   12.238%   $59.9575   $59.96   $59.95   $60.00  
  Purchase #4 $219.46   5.441%   $231.4008   $231.40   $231.40   $231.40  
  Purchase #5 $223.90   7.748%   $241.2478   $241.25   $241.25   $241.20  
  Purchase #6 $26.35   9.572%   $28.8722   $28.87   $28.85   $28.90  
  Purchase #7 $90.74   11.791%   $101.4392   $101.44   $101.45   $101.40  
  7 purchase totals = $943.79       $1,015.9576   $1,015.96   $1,015.95   $1,016.00