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	$95.98	10.426%	$105.9869	$105.99	$106.00	$106.00
Purchase #2	$91.74	6.652%	$97.8425	$97.84	$97.85	$97.80
Purchase #3	$27.25	3.230%	$28.1302	$28.13	$28.15	$28.10
Purchase #4	$108.96	9.141%	$118.92	$118.92	$118.90	$118.90
Purchase #5	$66.69	6.147%	$70.7894	$70.79	$70.80	$70.80
Purchase #6	$53.38	10.731%	$59.1082	$59.11	$59.10	$59.10
Purchase #7	$167.66	10.817%	$185.7958	$185.80	$185.80	$185.80
7 purchase totals =	$611.66		$666.5730	$666.58	$666.60	$666.50