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	$179.63	6.635%	$191.5485	$191.55	$191.55	$191.50
Purchase #2	$64.81	3.838%	$67.2974	$67.30	$67.30	$67.30
Purchase #3	$166.73	10.637%	$184.4651	$184.47	$184.45	$184.50
Purchase #4	$48.31	5.433%	$50.9347	$50.93	$50.95	$50.90
Purchase #5	$139.58	7.683%	$150.3039	$150.30	$150.30	$150.30
Purchase #6	$248.91	7.639%	$267.9242	$267.92	$267.90	$267.90
Purchase #7	$88.36	3.687%	$91.6178	$91.62	$91.60	$91.60
7 purchase totals =	$936.33		$1,004.0916	$1,004.09	$1,004.05	$1,004.00