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	$137.75	9.845%	$151.3115	$151.31	$151.30	$151.30
Purchase #2	$162.95	10.378%	$179.861	$179.86	$179.85	$179.90
Purchase #3	$82.40	7.210%	$88.341	$88.34	$88.35	$88.30
Purchase #4	$18.91	10.280%	$20.8539	$20.85	$20.85	$20.90
Purchase #5	$46.88	9.647%	$51.4025	$51.40	$51.40	$51.40
Purchase #6	$164.58	10.502%	$181.8642	$181.86	$181.85	$181.90
Purchase #7	$154.58	7.167%	$165.6587	$165.66	$165.65	$165.70
7 purchase totals =	$768.05		$839.2928	$839.28	$839.25	$839.40