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 $205.29   13.794%   $233.6077   $233.61   $233.60   $233.60  
  Purchase #2 $10.65   13.212%   $12.0571   $12.06   $12.05   $12.10  
  Purchase #3 $69.44   6.554%   $73.9911   $73.99   $74.00   $74.00  
  Purchase #4 $69.90   7.656%   $75.2515   $75.25   $75.25   $75.30  
  Purchase #5 $246.40   9.392%   $269.5419   $269.54   $269.55   $269.50  
  Purchase #6 $36.64   5.811%   $38.7692   $38.77   $38.75   $38.80  
  Purchase #7 $29.95   4.168%   $31.1983   $31.20   $31.20   $31.20  
  7 purchase totals = $668.27       $734.4168   $734.42   $734.40   $734.50