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	$191.82	9.608%	$210.2501	$210.25	$210.25	$210.30
Purchase #2	$245.61	10.268%	$270.8292	$270.83	$270.85	$270.80
Purchase #3	$86.50	7.205%	$92.7323	$92.73	$92.75	$92.70
Purchase #4	$86.37	3.195%	$89.1295	$89.13	$89.15	$89.10
Purchase #5	$149.96	5.529%	$158.2513	$158.25	$158.25	$158.30
Purchase #6	$187.38	5.307%	$197.3243	$197.32	$197.30	$197.30
Purchase #7	$73.78	6.838%	$78.8251	$78.83	$78.85	$78.80
7 purchase totals =	$1,021.42		$1,097.3418	$1,097.34	$1,097.40	$1,097.30