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	$42.79	6.544%	$45.5902	$45.59	$45.60	$45.60
Purchase #2	$60.29	4.695%	$63.1206	$63.12	$63.10	$63.10
Purchase #3	$238.84	10.251%	$263.3235	$263.32	$263.30	$263.30
Purchase #4	$95.59	3.784%	$99.2071	$99.21	$99.20	$99.20
Purchase #5	$141.25	8.147%	$152.7576	$152.76	$152.75	$152.80
Purchase #6	$37.50	5.618%	$39.6068	$39.61	$39.60	$39.60
Purchase #7	$226.29	8.827%	$246.2646	$246.26	$246.25	$246.30
7 purchase totals =	$842.55		$909.8704	$909.87	$909.80	$909.90