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	$165.86	4.617%	$173.5178	$173.52	$173.50	$173.50
Purchase #2	$136.45	11.773%	$152.5143	$152.51	$152.50	$152.50
Purchase #3	$157.85	7.869%	$170.2712	$170.27	$170.25	$170.30
Purchase #4	$17.54	6.315%	$18.6477	$18.65	$18.65	$18.60
Purchase #5	$167.33	7.492%	$179.8664	$179.87	$179.85	$179.90
Purchase #6	$143.88	11.450%	$160.3543	$160.35	$160.35	$160.40
Purchase #7	$81.45	11.220%	$90.5887	$90.59	$90.60	$90.60
7 purchase totals =	$870.36		$945.7604	$945.76	$945.70	$945.80