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	$151.83	9.521%	$166.2857	$166.29	$166.30	$166.30
Purchase #2	$32.98	12.548%	$37.1183	$37.12	$37.10	$37.10
Purchase #3	$80.60	6.834%	$86.1082	$86.11	$86.10	$86.10
Purchase #4	$144.77	9.166%	$158.0396	$158.04	$158.05	$158.00
Purchase #5	$104.28	5.206%	$109.7088	$109.71	$109.70	$109.70
Purchase #6	$66.71	8.281%	$72.2343	$72.23	$72.25	$72.20
Purchase #7	$32.67	7.253%	$35.0396	$35.04	$35.05	$35.00
7 purchase totals =	$613.84		$664.5345	$664.54	$664.55	$664.40