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	$30.49	13.212%	$34.5183	$34.52	$34.50	$34.50
Purchase #2	$163.29	5.418%	$172.1371	$172.14	$172.15	$172.10
Purchase #3	$79.37	3.600%	$82.2273	$82.23	$82.25	$82.20
Purchase #4	$14.78	7.855%	$15.941	$15.94	$15.95	$15.90
Purchase #5	$62.39	6.473%	$66.4285	$66.43	$66.45	$66.40
Purchase #6	$223.98	5.314%	$235.8823	$235.88	$235.90	$235.90
Purchase #7	$218.42	11.402%	$243.3242	$243.32	$243.30	$243.30
7 purchase totals =	$792.72		$850.4587	$850.46	$850.50	$850.30