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	$155.31	6.871%	$165.9814	$165.98	$166.00	$166.00
Purchase #2	$51.80	3.439%	$53.5814	$53.58	$53.60	$53.60
Purchase #3	$63.86	11.758%	$71.3687	$71.37	$71.35	$71.40
Purchase #4	$182.43	10.667%	$201.8898	$201.89	$201.90	$201.90
Purchase #5	$44.98	9.578%	$49.2882	$49.29	$49.30	$49.30
Purchase #6	$37.76	4.132%	$39.3202	$39.32	$39.30	$39.30
Purchase #7	$52.51	4.216%	$54.7238	$54.72	$54.70	$54.70
7 purchase totals =	$588.65		$636.1535	$636.15	$636.15	$636.20