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	$25.86	11.629%	$28.8673	$28.87	$28.85	$28.90
Purchase #2	$99.51	12.324%	$111.7736	$111.77	$111.75	$111.80
Purchase #3	$236.65	8.409%	$256.5499	$256.55	$256.55	$256.50
Purchase #4	$119.31	8.399%	$129.3308	$129.33	$129.35	$129.30
Purchase #5	$163.57	5.626%	$172.7724	$172.77	$172.75	$172.80
Purchase #6	$199.50	4.447%	$208.3718	$208.37	$208.35	$208.40
Purchase #7	$138.38	4.202%	$144.1947	$144.19	$144.20	$144.20
7 purchase totals =	$982.78		$1,051.8605	$1,051.85	$1,051.80	$1,051.90