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	$54.77	4.663%	$57.3239	$57.32	$57.30	$57.30
Purchase #2	$50.64	8.169%	$54.7768	$54.78	$54.80	$54.80
Purchase #3	$248.90	6.424%	$264.8893	$264.89	$264.90	$264.90
Purchase #4	$157.59	3.589%	$163.2459	$163.25	$163.25	$163.20
Purchase #5	$39.85	9.359%	$43.5796	$43.58	$43.60	$43.60
Purchase #6	$151.28	11.479%	$168.6454	$168.65	$168.65	$168.60
Purchase #7	$120.36	5.466%	$126.9389	$126.94	$126.95	$126.90
7 purchase totals =	$823.39		$879.3998	$879.41	$879.45	$879.30