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	$175.83	7.410%	$188.859	$188.86	$188.85	$188.90
Purchase #2	$83.50	10.335%	$92.1297	$92.13	$92.15	$92.10
Purchase #3	$91.90	8.764%	$99.9541	$99.95	$99.95	$100.00
Purchase #4	$154.87	8.335%	$167.7784	$167.78	$167.80	$167.80
Purchase #5	$211.97	5.560%	$223.7555	$223.76	$223.75	$223.80
Purchase #6	$156.40	7.436%	$168.0299	$168.03	$168.05	$168.00
Purchase #7	$30.84	7.826%	$33.2535	$33.25	$33.25	$33.30
7 purchase totals =	$905.31		$973.7601	$973.76	$973.80	$973.90