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	$72.67	8.278%	$78.6856	$78.69	$78.70	$78.70
Purchase #2	$57.38	6.617%	$61.1768	$61.18	$61.20	$61.20
Purchase #3	$96.48	7.646%	$103.8569	$103.86	$103.85	$103.90
Purchase #4	$54.29	8.487%	$58.8976	$58.90	$58.90	$58.90
Purchase #5	$54.50	8.815%	$59.3042	$59.30	$59.30	$59.30
Purchase #6	$64.38	3.287%	$66.4962	$66.50	$66.50	$66.50
Purchase #7	$76.63	6.609%	$81.6945	$81.69	$81.70	$81.70
7 purchase totals =	$476.33		$510.1118	$510.12	$510.15	$510.20