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	$83.86	6.842%	$89.5977	$89.60	$89.60	$89.60
Purchase #2	$29.73	9.633%	$32.5939	$32.59	$32.60	$32.60
Purchase #3	$85.48	8.562%	$92.7988	$92.80	$92.80	$92.80
Purchase #4	$182.56	7.744%	$196.6974	$196.70	$196.70	$196.70
Purchase #5	$108.48	10.647%	$120.0299	$120.03	$120.05	$120.00
Purchase #6	$159.34	11.291%	$177.3311	$177.33	$177.35	$177.30
Purchase #7	$47.66	5.631%	$50.3437	$50.34	$50.35	$50.30
7 purchase totals =	$697.11		$759.3925	$759.39	$759.45	$759.30