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	$83.45	8.419%	$90.4757	$90.48	$90.50	$90.50
Purchase #2	$21.88	3.780%	$22.7071	$22.71	$22.70	$22.70
Purchase #3	$68.41	4.563%	$71.5315	$71.53	$71.55	$71.50
Purchase #4	$65.74	11.799%	$73.4967	$73.50	$73.50	$73.50
Purchase #5	$60.68	8.818%	$66.0308	$66.03	$66.05	$66.00
Purchase #6	$151.45	3.319%	$156.4766	$156.48	$156.50	$156.50
Purchase #7	$109.64	13.631%	$124.585	$124.59	$124.60	$124.60
7 purchase totals =	$561.25		$605.3034	$605.32	$605.40	$605.30