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	$99.38	6.427%	$105.7672	$105.77	$105.75	$105.80
Purchase #2	$124.28	3.336%	$128.426	$128.43	$128.45	$128.40
Purchase #3	$89.43	13.551%	$101.5487	$101.55	$101.55	$101.50
Purchase #4	$142.94	3.147%	$147.4383	$147.44	$147.45	$147.40
Purchase #5	$246.49	4.633%	$257.9099	$257.91	$257.90	$257.90
Purchase #6	$137.78	12.547%	$155.0673	$155.07	$155.05	$155.10
Purchase #7	$179.40	8.563%	$194.762	$194.76	$194.75	$194.80
7 purchase totals =	$1,019.70		$1,090.9194	$1,090.93	$1,090.90	$1,090.90