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	$122.97	7.194%	$131.8165	$131.82	$131.80	$131.80
Purchase #2	$10.67	12.761%	$12.0316	$12.03	$12.05	$12.00
Purchase #3	$154.58	11.501%	$172.3582	$172.36	$172.35	$172.40
Purchase #4	$99.57	5.349%	$104.896	$104.90	$104.90	$104.90
Purchase #5	$195.74	13.250%	$221.6756	$221.68	$221.70	$221.70
Purchase #6	$91.43	12.136%	$102.5259	$102.53	$102.55	$102.50
Purchase #7	$32.88	12.825%	$37.0969	$37.10	$37.10	$37.10
7 purchase totals =	$707.84		$782.4007	$782.42	$782.45	$782.40