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	$129.67	10.194%	$142.8886	$142.89	$142.90	$142.90
Purchase #2	$61.50	4.434%	$64.2269	$64.23	$64.25	$64.20
Purchase #3	$57.30	5.174%	$60.2647	$60.26	$60.25	$60.30
Purchase #4	$174.79	9.171%	$190.82	$190.82	$190.80	$190.80
Purchase #5	$163.94	3.433%	$169.5681	$169.57	$169.55	$169.60
Purchase #6	$25.75	10.398%	$28.4275	$28.43	$28.45	$28.40
Purchase #7	$156.96	6.255%	$166.7778	$166.78	$166.80	$166.80
7 purchase totals =	$769.91		$822.9736	$822.98	$823.00	$823.00