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	$100.73	13.767%	$114.5975	$114.60	$114.60	$114.60
Purchase #2	$72.93	13.140%	$82.513	$82.51	$82.50	$82.50
Purchase #3	$92.53	13.743%	$105.2464	$105.25	$105.25	$105.20
Purchase #4	$18.92	9.532%	$20.7235	$20.72	$20.70	$20.70
Purchase #5	$130.77	3.377%	$135.1861	$135.19	$135.20	$135.20
Purchase #6	$80.65	12.446%	$90.6877	$90.69	$90.70	$90.70
Purchase #7	$170.94	8.318%	$185.1588	$185.16	$185.15	$185.20
7 purchase totals =	$667.47		$734.1130	$734.12	$734.10	$734.10