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	$78.43	5.603%	$82.8244	$82.82	$82.80	$82.80
Purchase #2	$193.54	8.838%	$210.6451	$210.65	$210.65	$210.60
Purchase #3	$146.57	4.104%	$152.5852	$152.59	$152.60	$152.60
Purchase #4	$132.66	6.112%	$140.7682	$140.77	$140.75	$140.80
Purchase #5	$30.60	3.127%	$31.5569	$31.56	$31.55	$31.60
Purchase #6	$108.46	9.485%	$118.7474	$118.75	$118.75	$118.70
Purchase #7	$151.76	9.313%	$165.8934	$165.89	$165.90	$165.90
7 purchase totals =	$842.02		$903.0206	$903.03	$903.00	$903.00