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	$191.99	3.163%	$198.0626	$198.06	$198.05	$198.10
Purchase #2	$78.55	13.808%	$89.3962	$89.40	$89.40	$89.40
Purchase #3	$217.79	9.335%	$238.1207	$238.12	$238.10	$238.10
Purchase #4	$43.54	13.589%	$49.4567	$49.46	$49.45	$49.50
Purchase #5	$52.36	3.455%	$54.169	$54.17	$54.15	$54.20
Purchase #6	$29.67	8.488%	$32.1884	$32.19	$32.20	$32.20
Purchase #7	$60.89	10.303%	$67.1635	$67.16	$67.15	$67.20
7 purchase totals =	$674.79		$728.5571	$728.56	$728.50	$728.70