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	$147.47	3.675%	$152.8895	$152.89	$152.90	$152.90
Purchase #2	$113.74	8.318%	$123.2009	$123.20	$123.20	$123.20
Purchase #3	$103.50	10.792%	$114.6697	$114.67	$114.65	$114.70
Purchase #4	$35.57	13.625%	$40.4164	$40.42	$40.40	$40.40
Purchase #5	$74.38	8.585%	$80.7655	$80.77	$80.75	$80.80
Purchase #6	$216.85	3.171%	$223.7263	$223.73	$223.75	$223.70
Purchase #7	$240.69	4.353%	$251.1672	$251.17	$251.15	$251.20
7 purchase totals =	$932.20		$986.8355	$986.85	$986.80	$986.90