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	$96.30	3.109%	$99.294	$99.29	$99.30	$99.30
Purchase #2	$87.32	8.341%	$94.6034	$94.60	$94.60	$94.60
Purchase #3	$148.89	9.280%	$162.707	$162.71	$162.70	$162.70
Purchase #4	$122.28	9.284%	$133.6325	$133.63	$133.65	$133.60
Purchase #5	$69.45	13.485%	$78.8153	$78.82	$78.80	$78.80
Purchase #6	$145.81	10.604%	$161.2717	$161.27	$161.25	$161.30
Purchase #7	$77.65	6.360%	$82.5885	$82.59	$82.60	$82.60
7 purchase totals =	$747.70		$812.9124	$812.91	$812.90	$812.90