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	$78.64	12.646%	$88.5848	$88.58	$88.60	$88.60
Purchase #2	$246.96	4.871%	$258.9894	$258.99	$259.00	$259.00
Purchase #3	$67.42	6.329%	$71.687	$71.69	$71.70	$71.70
Purchase #4	$71.58	11.170%	$79.5755	$79.58	$79.60	$79.60
Purchase #5	$116.50	10.625%	$128.8781	$128.88	$128.90	$128.90
Purchase #6	$82.73	3.352%	$85.5031	$85.50	$85.50	$85.50
Purchase #7	$77.72	7.445%	$83.5063	$83.51	$83.50	$83.50
7 purchase totals =	$741.55		$796.7242	$796.73	$796.80	$796.80