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	$230.57	5.141%	$242.4236	$242.42	$242.40	$242.40
Purchase #2	$136.71	12.655%	$154.0107	$154.01	$154.00	$154.00
Purchase #3	$120.41	6.679%	$128.4522	$128.45	$128.45	$128.50
Purchase #4	$5.91	9.576%	$6.4759	$6.48	$6.50	$6.50
Purchase #5	$87.77	9.419%	$96.0371	$96.04	$96.05	$96.00
Purchase #6	$250.83	9.753%	$275.2934	$275.29	$275.30	$275.30
Purchase #7	$170.75	4.690%	$178.7582	$178.76	$178.75	$178.80
7 purchase totals =	$1,002.95		$1,081.4511	$1,081.45	$1,081.45	$1,081.50