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	$121.58	10.532%	$134.3848	$134.38	$134.40	$134.40
Purchase #2	$155.87	8.280%	$168.776	$168.78	$168.80	$168.80
Purchase #3	$98.48	11.299%	$109.6073	$109.61	$109.60	$109.60
Purchase #4	$184.83	8.302%	$200.1746	$200.17	$200.15	$200.20
Purchase #5	$117.77	9.207%	$128.6131	$128.61	$128.60	$128.60
Purchase #6	$134.41	5.658%	$142.0149	$142.01	$142.00	$142.00
Purchase #7	$143.50	9.182%	$156.6762	$156.68	$156.70	$156.70
7 purchase totals =	$956.44		$1,040.2469	$1,040.24	$1,040.25	$1,040.30