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 $219.60   10.176%   $241.9465   $241.95   $241.95   $241.90  
  Purchase #2 $103.41   7.268%   $110.9258   $110.93   $110.95   $110.90  
  Purchase #3 $189.79   12.868%   $214.2122   $214.21   $214.20   $214.20  
  Purchase #4 $136.53   9.556%   $149.5768   $149.58   $149.60   $149.60  
  Purchase #5 $200.90   3.819%   $208.5724   $208.57   $208.55   $208.60  
  Purchase #6 $193.51   3.854%   $200.9679   $200.97   $200.95   $201.00  
  Purchase #7 $120.41   5.293%   $126.7833   $126.78   $126.80   $126.80  
  7 purchase totals = $1,164.15       $1,252.9849   $1,252.99   $1,253.00   $1,253.00