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	$158.27	13.455%	$179.5652	$179.57	$179.55	$179.60
Purchase #2	$244.72	12.597%	$275.5474	$275.55	$275.55	$275.50
Purchase #3	$82.94	10.745%	$91.8519	$91.85	$91.85	$91.90
Purchase #4	$205.43	7.249%	$220.3216	$220.32	$220.30	$220.30
Purchase #5	$126.32	4.796%	$132.3783	$132.38	$132.40	$132.40
Purchase #6	$105.53	10.113%	$116.2022	$116.20	$116.20	$116.20
Purchase #7	$170.84	6.765%	$182.3973	$182.40	$182.40	$182.40
7 purchase totals =	$1,094.05		$1,198.2639	$1,198.27	$1,198.25	$1,198.30