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	$116.66	6.254%	$123.9559	$123.96	$123.95	$124.00
Purchase #2	$61.53	4.321%	$64.1887	$64.19	$64.20	$64.20
Purchase #3	$66.92	10.275%	$73.796	$73.80	$73.80	$73.80
Purchase #4	$46.73	12.280%	$52.4684	$52.47	$52.45	$52.50
Purchase #5	$131.45	3.825%	$136.478	$136.48	$136.50	$136.50
Purchase #6	$75.45	8.848%	$82.1258	$82.13	$82.15	$82.10
Purchase #7	$53.98	11.800%	$60.3496	$60.35	$60.35	$60.30
7 purchase totals =	$552.72		$593.3624	$593.38	$593.40	$593.40