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	$212.30	13.152%	$240.2217	$240.22	$240.20	$240.20
Purchase #2	$221.49	6.719%	$236.3719	$236.37	$236.35	$236.40
Purchase #3	$162.66	13.556%	$184.7102	$184.71	$184.70	$184.70
Purchase #4	$72.63	6.418%	$77.2914	$77.29	$77.30	$77.30
Purchase #5	$103.59	5.288%	$109.0678	$109.07	$109.05	$109.10
Purchase #6	$30.81	6.327%	$32.7593	$32.76	$32.75	$32.80
Purchase #7	$95.34	4.301%	$99.4406	$99.44	$99.45	$99.40
7 purchase totals =	$898.82		$979.8629	$979.86	$979.80	$979.90