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	$248.78	3.833%	$258.3157	$258.32	$258.30	$258.30
Purchase #2	$102.95	11.258%	$114.5401	$114.54	$114.55	$114.50
Purchase #3	$121.76	5.282%	$128.1914	$128.19	$128.20	$128.20
Purchase #4	$118.59	10.585%	$131.1428	$131.14	$131.15	$131.10
Purchase #5	$131.77	8.343%	$142.7636	$142.76	$142.75	$142.80
Purchase #6	$124.31	7.566%	$133.7153	$133.72	$133.70	$133.70
Purchase #7	$37.99	12.768%	$42.8406	$42.84	$42.85	$42.80
7 purchase totals =	$886.15		$951.5095	$951.51	$951.50	$951.40