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	$213.64	9.446%	$233.8204	$233.82	$233.80	$233.80
Purchase #2	$131.95	10.317%	$145.5633	$145.56	$145.55	$145.60
Purchase #3	$49.93	12.476%	$56.1593	$56.16	$56.15	$56.20
Purchase #4	$35.92	13.527%	$40.7789	$40.78	$40.80	$40.80
Purchase #5	$96.34	4.579%	$100.7514	$100.75	$100.75	$100.80
Purchase #6	$228.48	9.843%	$250.9693	$250.97	$250.95	$251.00
Purchase #7	$92.74	8.817%	$100.9169	$100.92	$100.90	$100.90
7 purchase totals =	$849.00		$928.9595	$928.96	$928.90	$929.10