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	$74.90	5.253%	$78.8345	$78.83	$78.85	$78.80
Purchase #2	$220.29	3.331%	$227.6279	$227.63	$227.65	$227.60
Purchase #3	$111.57	8.502%	$121.0557	$121.06	$121.05	$121.10
Purchase #4	$191.60	4.700%	$200.6052	$200.61	$200.60	$200.60
Purchase #5	$42.68	4.700%	$44.686	$44.69	$44.70	$44.70
Purchase #6	$148.68	13.197%	$168.3013	$168.30	$168.30	$168.30
Purchase #7	$146.71	10.178%	$161.6421	$161.64	$161.65	$161.60
7 purchase totals =	$936.43		$1,002.7527	$1,002.76	$1,002.80	$1,002.70