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	$52.38	4.284%	$54.624	$54.62	$54.60	$54.60
Purchase #2	$126.36	3.163%	$130.3568	$130.36	$130.35	$130.40
Purchase #3	$137.52	9.454%	$150.5211	$150.52	$150.50	$150.50
Purchase #4	$78.89	3.761%	$81.8571	$81.86	$81.85	$81.90
Purchase #5	$237.76	4.686%	$248.9014	$248.90	$248.90	$248.90
Purchase #6	$16.61	9.445%	$18.1788	$18.18	$18.20	$18.20
Purchase #7	$130.53	11.572%	$145.6349	$145.63	$145.65	$145.60
7 purchase totals =	$780.05		$830.0741	$830.07	$830.05	$830.10