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	$25.48	10.546%	$28.1671	$28.17	$28.15	$28.20
Purchase #2	$160.88	12.364%	$180.7712	$180.77	$180.75	$180.80
Purchase #3	$44.89	9.842%	$49.3081	$49.31	$49.30	$49.30
Purchase #4	$121.67	5.423%	$128.2682	$128.27	$128.25	$128.30
Purchase #5	$73.27	13.471%	$83.1402	$83.14	$83.15	$83.10
Purchase #6	$132.60	9.109%	$144.6785	$144.68	$144.70	$144.70
Purchase #7	$77.73	11.311%	$86.522	$86.52	$86.50	$86.50
7 purchase totals =	$636.52		$700.8553	$700.86	$700.80	$700.90