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 $214.96   12.521%   $241.8751   $241.88   $241.90   $241.90  
  Purchase #2 $22.44   13.860%   $25.5502   $25.55   $25.55   $25.60  
  Purchase #3 $32.44   7.718%   $34.9437   $34.94   $34.95   $34.90  
  Purchase #4 $200.48   10.686%   $221.9033   $221.90   $221.90   $221.90  
  Purchase #5 $176.57   5.843%   $186.887   $186.89   $186.90   $186.90  
  Purchase #6 $208.70   10.472%   $230.5551   $230.56   $230.55   $230.60  
  Purchase #7 $6.87   4.866%   $7.2043   $7.20   $7.20   $7.20  
  7 purchase totals = $862.46       $948.9187   $948.92   $948.95   $949.00