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	$206.77	7.102%	$221.4548	$221.45	$221.45	$221.50
Purchase #2	$68.83	7.596%	$74.0583	$74.06	$74.05	$74.10
Purchase #3	$57.74	3.298%	$59.6443	$59.64	$59.65	$59.60
Purchase #4	$38.73	9.671%	$42.4756	$42.48	$42.50	$42.50
Purchase #5	$128.76	10.129%	$141.8021	$141.80	$141.80	$141.80
Purchase #6	$188.53	3.705%	$195.515	$195.52	$195.50	$195.50
Purchase #7	$93.47	10.498%	$103.2825	$103.28	$103.30	$103.30
7 purchase totals =	$782.83		$838.2326	$838.23	$838.25	$838.30