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	$25.63	11.451%	$28.5649	$28.56	$28.55	$28.60
Purchase #2	$46.89	4.268%	$48.8913	$48.89	$48.90	$48.90
Purchase #3	$70.29	3.297%	$72.6075	$72.61	$72.60	$72.60
Purchase #4	$105.53	7.570%	$113.5186	$113.52	$113.50	$113.50
Purchase #5	$123.88	12.207%	$139.002	$139.00	$139.00	$139.00
Purchase #6	$170.89	4.555%	$178.674	$178.67	$178.65	$178.70
Purchase #7	$60.62	13.197%	$68.62	$68.62	$68.60	$68.60
7 purchase totals =	$603.73		$649.8783	$649.87	$649.80	$649.90