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	$223.63	8.142%	$241.838	$241.84	$241.85	$241.80
Purchase #2	$183.89	9.267%	$200.9311	$200.93	$200.95	$200.90
Purchase #3	$150.33	3.262%	$155.2338	$155.23	$155.25	$155.20
Purchase #4	$123.42	4.787%	$129.3281	$129.33	$129.35	$129.30
Purchase #5	$72.39	6.210%	$76.8854	$76.89	$76.90	$76.90
Purchase #6	$125.62	9.697%	$137.8014	$137.80	$137.80	$137.80
Purchase #7	$31.86	12.653%	$35.8912	$35.89	$35.90	$35.90
7 purchase totals =	$911.14		$977.9090	$977.91	$978.00	$977.80