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	$52.90	12.384%	$59.4511	$59.45	$59.45	$59.50
Purchase #2	$70.36	6.835%	$75.1691	$75.17	$75.15	$75.20
Purchase #3	$145.52	13.361%	$164.9629	$164.96	$164.95	$165.00
Purchase #4	$115.33	10.697%	$127.6669	$127.67	$127.65	$127.70
Purchase #5	$224.68	13.567%	$255.1623	$255.16	$255.15	$255.20
Purchase #6	$112.79	6.285%	$119.8789	$119.88	$119.90	$119.90
Purchase #7	$231.63	8.642%	$251.6475	$251.65	$251.65	$251.60
7 purchase totals =	$953.21		$1,053.9387	$1,053.94	$1,053.90	$1,054.10