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 $30.50   10.606%   $33.7348   $33.73   $33.75   $33.70  
  Purchase #2 $227.78   13.546%   $258.6351   $258.64   $258.65   $258.60  
  Purchase #3 $126.97   5.819%   $134.3584   $134.36   $134.35   $134.40  
  Purchase #4 $118.81   12.674%   $133.868   $133.87   $133.85   $133.90  
  Purchase #5 $130.40   10.802%   $144.4858   $144.49   $144.50   $144.50  
  Purchase #6 $237.49   5.563%   $250.7016   $250.70   $250.70   $250.70  
  Purchase #7 $201.54   8.472%   $218.6145   $218.61   $218.60   $218.60  
  7 purchase totals = $1,073.49       $1,174.3982   $1,174.40   $1,174.40   $1,174.40