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	$141.50	4.441%	$147.784	$147.78	$147.80	$147.80
Purchase #2	$236.65	11.341%	$263.4885	$263.49	$263.50	$263.50
Purchase #3	$80.37	10.602%	$88.8908	$88.89	$88.90	$88.90
Purchase #4	$59.85	3.770%	$62.1063	$62.11	$62.10	$62.10
Purchase #5	$219.42	10.739%	$242.9835	$242.98	$243.00	$243.00
Purchase #6	$137.87	5.456%	$145.3922	$145.39	$145.40	$145.40
Purchase #7	$131.25	5.243%	$138.1314	$138.13	$138.15	$138.10
7 purchase totals =	$1,006.91		$1,088.7767	$1,088.77	$1,088.85	$1,088.80