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	$166.91	5.515%	$176.1151	$176.12	$176.10	$176.10
Purchase #2	$77.34	5.168%	$81.3369	$81.34	$81.35	$81.30
Purchase #3	$225.40	10.638%	$249.3781	$249.38	$249.40	$249.40
Purchase #4	$51.54	3.118%	$53.147	$53.15	$53.15	$53.10
Purchase #5	$141.54	7.300%	$151.8724	$151.87	$151.85	$151.90
Purchase #6	$224.71	7.769%	$242.1677	$242.17	$242.15	$242.20
Purchase #7	$34.90	10.454%	$38.5484	$38.55	$38.55	$38.50
7 purchase totals =	$922.34		$992.5656	$992.58	$992.55	$992.50