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	$59.56	12.789%	$67.1771	$67.18	$67.20	$67.20
Purchase #2	$209.66	9.439%	$229.4498	$229.45	$229.45	$229.40
Purchase #3	$42.62	6.328%	$45.317	$45.32	$45.30	$45.30
Purchase #4	$76.82	7.629%	$82.6806	$82.68	$82.70	$82.70
Purchase #5	$188.71	10.213%	$207.983	$207.98	$208.00	$208.00
Purchase #6	$238.89	11.364%	$266.0375	$266.04	$266.05	$266.00
Purchase #7	$32.67	9.831%	$35.8818	$35.88	$35.90	$35.90
7 purchase totals =	$848.93		$934.5268	$934.53	$934.60	$934.50