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	$173.50	10.624%	$191.9326	$191.93	$191.95	$191.90
Purchase #2	$143.84	9.692%	$157.781	$157.78	$157.80	$157.80
Purchase #3	$45.98	6.328%	$48.8896	$48.89	$48.90	$48.90
Purchase #4	$160.89	7.429%	$172.8425	$172.84	$172.85	$172.80
Purchase #5	$18.46	12.194%	$20.711	$20.71	$20.70	$20.70
Purchase #6	$136.29	3.649%	$141.2632	$141.26	$141.25	$141.30
Purchase #7	$100.74	4.856%	$105.6319	$105.63	$105.65	$105.60
7 purchase totals =	$779.70		$839.0518	$839.04	$839.10	$839.00