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	$73.65	6.580%	$78.4962	$78.50	$78.50	$78.50
Purchase #2	$100.55	8.116%	$108.7106	$108.71	$108.70	$108.70
Purchase #3	$154.47	7.842%	$166.5835	$166.58	$166.60	$166.60
Purchase #4	$235.60	3.146%	$243.012	$243.01	$243.00	$243.00
Purchase #5	$70.31	3.641%	$72.87	$72.87	$72.85	$72.90
Purchase #6	$58.55	3.268%	$60.4634	$60.46	$60.45	$60.50
Purchase #7	$100.29	6.575%	$106.8841	$106.88	$106.90	$106.90
7 purchase totals =	$793.42		$837.0198	$837.01	$837.00	$837.10