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	$231.63	5.158%	$243.5775	$243.58	$243.60	$243.60
Purchase #2	$134.43	13.731%	$152.8886	$152.89	$152.90	$152.90
Purchase #3	$62.39	13.327%	$70.7047	$70.70	$70.70	$70.70
Purchase #4	$32.51	4.299%	$33.9076	$33.91	$33.90	$33.90
Purchase #5	$210.55	5.570%	$222.2776	$222.28	$222.30	$222.30
Purchase #6	$152.52	10.832%	$169.041	$169.04	$169.05	$169.00
Purchase #7	$77.77	6.479%	$82.8087	$82.81	$82.80	$82.80
7 purchase totals =	$901.80		$975.2057	$975.21	$975.25	$975.20