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	$82.42	10.284%	$90.8961	$90.90	$90.90	$90.90
Purchase #2	$69.42	5.242%	$73.059	$73.06	$73.05	$73.10
Purchase #3	$233.50	13.813%	$265.7534	$265.75	$265.75	$265.80
Purchase #4	$76.52	8.324%	$82.8895	$82.89	$82.90	$82.90
Purchase #5	$29.90	8.334%	$32.3919	$32.39	$32.40	$32.40
Purchase #6	$144.74	5.187%	$152.2477	$152.25	$152.25	$152.20
Purchase #7	$129.61	8.234%	$140.2821	$140.28	$140.30	$140.30
7 purchase totals =	$766.11		$837.5197	$837.52	$837.55	$837.60