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	$45.65	11.285%	$50.8016	$50.80	$50.80	$50.80
Purchase #2	$34.33	9.466%	$37.5797	$37.58	$37.60	$37.60
Purchase #3	$24.85	9.582%	$27.2311	$27.23	$27.25	$27.20
Purchase #4	$162.26	10.257%	$178.903	$178.90	$178.90	$178.90
Purchase #5	$45.82	9.241%	$50.0542	$50.05	$50.05	$50.10
Purchase #6	$148.52	6.535%	$158.2258	$158.23	$158.25	$158.20
Purchase #7	$208.71	10.868%	$231.3926	$231.39	$231.40	$231.40
7 purchase totals =	$670.14		$734.1880	$734.18	$734.25	$734.20