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	$85.27	6.198%	$90.555	$90.56	$90.55	$90.60
Purchase #2	$59.88	8.194%	$64.7866	$64.79	$64.80	$64.80
Purchase #3	$54.36	10.562%	$60.1015	$60.10	$60.10	$60.10
Purchase #4	$164.67	10.748%	$182.3687	$182.37	$182.35	$182.40
Purchase #5	$128.40	12.344%	$144.2497	$144.25	$144.25	$144.20
Purchase #6	$144.91	3.741%	$150.3311	$150.33	$150.35	$150.30
Purchase #7	$237.93	9.615%	$260.807	$260.81	$260.80	$260.80
7 purchase totals =	$875.42		$953.1996	$953.21	$953.20	$953.20