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	$19.82	4.710%	$20.7535	$20.75	$20.75	$20.80
Purchase #2	$98.41	11.132%	$109.365	$109.37	$109.35	$109.40
Purchase #3	$240.82	9.483%	$263.657	$263.66	$263.65	$263.70
Purchase #4	$151.85	4.638%	$158.8928	$158.89	$158.90	$158.90
Purchase #5	$225.42	7.622%	$242.6015	$242.60	$242.60	$242.60
Purchase #6	$46.78	11.855%	$52.3258	$52.33	$52.35	$52.30
Purchase #7	$88.87	12.765%	$100.2143	$100.21	$100.20	$100.20
7 purchase totals =	$871.97		$947.8099	$947.81	$947.80	$947.90