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	$170.53	5.336%	$179.6295	$179.63	$179.65	$179.60
Purchase #2	$130.50	7.199%	$139.8947	$139.89	$139.90	$139.90
Purchase #3	$100.54	4.570%	$105.1347	$105.13	$105.15	$105.10
Purchase #4	$156.39	6.392%	$166.3864	$166.39	$166.40	$166.40
Purchase #5	$225.83	9.292%	$246.8141	$246.81	$246.80	$246.80
Purchase #6	$216.89	8.343%	$234.9851	$234.99	$235.00	$235.00
Purchase #7	$142.93	4.181%	$148.9059	$148.91	$148.90	$148.90
7 purchase totals =	$1,143.61		$1,221.7504	$1,221.75	$1,221.80	$1,221.70