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	$31.35	3.332%	$32.3946	$32.39	$32.40	$32.40
Purchase #2	$144.43	5.639%	$152.5744	$152.57	$152.55	$152.60
Purchase #3	$78.36	12.599%	$88.2326	$88.23	$88.25	$88.20
Purchase #4	$210.28	4.194%	$219.0991	$219.10	$219.10	$219.10
Purchase #5	$190.98	10.198%	$210.4561	$210.46	$210.45	$210.50
Purchase #6	$98.72	11.117%	$109.6947	$109.69	$109.70	$109.70
Purchase #7	$87.40	13.196%	$98.9333	$98.93	$98.95	$98.90
7 purchase totals =	$841.52		$911.3848	$911.37	$911.40	$911.40