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	$39.33	7.679%	$42.3502	$42.35	$42.35	$42.40
Purchase #2	$173.87	3.223%	$179.4738	$179.47	$179.45	$179.50
Purchase #3	$55.56	4.250%	$57.9213	$57.92	$57.90	$57.90
Purchase #4	$90.31	4.411%	$94.2936	$94.29	$94.30	$94.30
Purchase #5	$68.99	11.304%	$76.7886	$76.79	$76.80	$76.80
Purchase #6	$98.81	10.203%	$108.8916	$108.89	$108.90	$108.90
Purchase #7	$191.95	7.432%	$206.2157	$206.22	$206.20	$206.20
7 purchase totals =	$718.82		$765.9348	$765.93	$765.90	$766.00