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	$87.68	13.163%	$99.2213	$99.22	$99.20	$99.20
Purchase #2	$219.32	6.611%	$233.8192	$233.82	$233.80	$233.80
Purchase #3	$211.94	4.513%	$221.5049	$221.50	$221.50	$221.50
Purchase #4	$171.63	11.481%	$191.3348	$191.33	$191.35	$191.30
Purchase #5	$153.28	3.107%	$158.0424	$158.04	$158.05	$158.00
Purchase #6	$36.36	11.574%	$40.5683	$40.57	$40.55	$40.60
Purchase #7	$240.27	5.735%	$254.0495	$254.05	$254.05	$254.00
7 purchase totals =	$1,120.48		$1,198.5404	$1,198.53	$1,198.50	$1,198.40