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	$123.64	3.572%	$128.0564	$128.06	$128.05	$128.10
Purchase #2	$226.76	10.381%	$250.3	$250.30	$250.30	$250.30
Purchase #3	$89.84	7.117%	$96.2339	$96.23	$96.25	$96.20
Purchase #4	$229.86	6.817%	$245.5296	$245.53	$245.55	$245.50
Purchase #5	$146.91	3.335%	$151.8094	$151.81	$151.80	$151.80
Purchase #6	$118.73	11.243%	$132.0788	$132.08	$132.10	$132.10
Purchase #7	$155.65	4.314%	$162.3647	$162.36	$162.35	$162.40
7 purchase totals =	$1,091.39		$1,166.3728	$1,166.37	$1,166.40	$1,166.40