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	$128.80	4.848%	$135.0442	$135.04	$135.05	$135.00
Purchase #2	$77.29	4.820%	$81.0154	$81.02	$81.00	$81.00
Purchase #3	$190.69	10.419%	$210.558	$210.56	$210.55	$210.60
Purchase #4	$208.96	6.861%	$223.2967	$223.30	$223.30	$223.30
Purchase #5	$164.46	11.332%	$183.0966	$183.10	$183.10	$183.10
Purchase #6	$11.92	8.155%	$12.8921	$12.89	$12.90	$12.90
Purchase #7	$111.78	10.831%	$123.8869	$123.89	$123.90	$123.90
7 purchase totals =	$893.90		$969.7899	$969.80	$969.80	$969.80