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	$52.77	9.386%	$57.723	$57.72	$57.70	$57.70
Purchase #2	$52.38	8.604%	$56.8868	$56.89	$56.90	$56.90
Purchase #3	$91.66	8.565%	$99.5107	$99.51	$99.50	$99.50
Purchase #4	$170.68	10.458%	$188.5297	$188.53	$188.55	$188.50
Purchase #5	$171.37	7.703%	$184.5706	$184.57	$184.55	$184.60
Purchase #6	$72.34	5.211%	$76.1096	$76.11	$76.10	$76.10
Purchase #7	$152.84	6.346%	$162.5392	$162.54	$162.55	$162.50
7 purchase totals =	$764.04		$825.8696	$825.87	$825.85	$825.80