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 $33.40   5.554%   $35.255   $35.26   $35.25   $35.30  
  Purchase #2 $17.87   9.663%   $19.5968   $19.60   $19.60   $19.60  
  Purchase #3 $191.51   5.312%   $201.683   $201.68   $201.70   $201.70  
  Purchase #4 $164.85   5.526%   $173.9596   $173.96   $173.95   $174.00  
  Purchase #5 $98.77   6.723%   $105.4103   $105.41   $105.40   $105.40  
  Purchase #6 $236.31   10.196%   $260.4042   $260.40   $260.40   $260.40  
  Purchase #7 $214.89   10.193%   $236.7937   $236.79   $236.80   $236.80  
  7 purchase totals = $957.60       $1,033.1026   $1,033.10   $1,033.10   $1,033.20