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	$89.93	11.411%	$100.1919	$100.19	$100.20	$100.20
Purchase #2	$86.75	12.686%	$97.7551	$97.76	$97.75	$97.80
Purchase #3	$209.52	6.439%	$223.011	$223.01	$223.00	$223.00
Purchase #4	$12.97	9.451%	$14.1958	$14.20	$14.20	$14.20
Purchase #5	$103.69	5.863%	$109.7693	$109.77	$109.75	$109.80
Purchase #6	$57.55	11.335%	$64.0733	$64.07	$64.05	$64.10
Purchase #7	$70.77	11.372%	$78.818	$78.82	$78.80	$78.80
7 purchase totals =	$631.18		$687.8144	$687.82	$687.75	$687.90