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	$180.40	10.230%	$198.8549	$198.85	$198.85	$198.90
Purchase #2	$85.37	5.435%	$90.0099	$90.01	$90.00	$90.00
Purchase #3	$71.32	11.801%	$79.7365	$79.74	$79.75	$79.70
Purchase #4	$171.26	12.670%	$192.9586	$192.96	$192.95	$193.00
Purchase #5	$159.71	4.514%	$166.9193	$166.92	$166.90	$166.90
Purchase #6	$205.61	4.342%	$214.5376	$214.54	$214.55	$214.50
Purchase #7	$34.53	7.492%	$37.117	$37.12	$37.10	$37.10
7 purchase totals =	$908.20		$980.1338	$980.14	$980.10	$980.10