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 $219.95   5.252%   $231.5018   $231.50   $231.50   $231.50  
  Purchase #2 $50.32   6.789%   $53.7362   $53.74   $53.75   $53.70  
  Purchase #3 $114.63   5.270%   $120.671   $120.67   $120.65   $120.70  
  Purchase #4 $18.80   9.345%   $20.5569   $20.56   $20.55   $20.60  
  Purchase #5 $179.85   9.769%   $197.4195   $197.42   $197.40   $197.40  
  Purchase #6 $81.44   7.119%   $87.2377   $87.24   $87.25   $87.20  
  Purchase #7 $31.44   4.740%   $32.9303   $32.93   $32.95   $32.90  
  7 purchase totals = $696.43       $744.0534   $744.06   $744.05   $744.00