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	$229.43	6.663%	$244.7169	$244.72	$244.70	$244.70
Purchase #2	$67.91	6.214%	$72.1299	$72.13	$72.15	$72.10
Purchase #3	$103.59	7.304%	$111.1562	$111.16	$111.15	$111.20
Purchase #4	$129.94	3.177%	$134.0682	$134.07	$134.05	$134.10
Purchase #5	$154.93	10.682%	$171.4796	$171.48	$171.50	$171.50
Purchase #6	$34.47	7.112%	$36.9215	$36.92	$36.90	$36.90
Purchase #7	$116.45	5.688%	$123.0737	$123.07	$123.05	$123.10
7 purchase totals =	$836.72		$893.5460	$893.55	$893.50	$893.60