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	$32.85	12.115%	$36.8298	$36.83	$36.85	$36.80
Purchase #2	$241.95	12.788%	$272.8906	$272.89	$272.90	$272.90
Purchase #3	$128.74	12.124%	$144.3484	$144.35	$144.35	$144.30
Purchase #4	$242.32	9.234%	$264.6958	$264.70	$264.70	$264.70
Purchase #5	$55.60	9.766%	$61.0299	$61.03	$61.05	$61.00
Purchase #6	$233.87	5.736%	$247.2848	$247.28	$247.30	$247.30
Purchase #7	$154.41	9.559%	$169.1701	$169.17	$169.15	$169.20
7 purchase totals =	$1,089.74		$1,196.2494	$1,196.25	$1,196.30	$1,196.20