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	$31.45	5.340%	$33.1294	$33.13	$33.15	$33.10
Purchase #2	$96.64	4.400%	$100.8922	$100.89	$100.90	$100.90
Purchase #3	$118.83	8.242%	$128.624	$128.62	$128.60	$128.60
Purchase #4	$126.29	10.358%	$139.3711	$139.37	$139.35	$139.40
Purchase #5	$126.41	4.223%	$131.7483	$131.75	$131.75	$131.70
Purchase #6	$237.41	10.624%	$262.6324	$262.63	$262.65	$262.60
Purchase #7	$82.96	10.565%	$91.7247	$91.72	$91.70	$91.70
7 purchase totals =	$819.99		$888.1221	$888.11	$888.10	$888.00