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	$239.42	3.625%	$248.099	$248.10	$248.10	$248.10
Purchase #2	$158.69	8.292%	$171.8486	$171.85	$171.85	$171.80
Purchase #3	$74.48	10.614%	$82.3853	$82.39	$82.40	$82.40
Purchase #4	$76.48	12.277%	$85.8694	$85.87	$85.85	$85.90
Purchase #5	$119.83	4.809%	$125.5926	$125.59	$125.60	$125.60
Purchase #6	$100.41	11.345%	$111.8015	$111.80	$111.80	$111.80
Purchase #7	$8.31	7.461%	$8.93	$8.93	$8.95	$8.90
7 purchase totals =	$777.62		$834.5264	$834.53	$834.55	$834.50