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	$179.39	3.784%	$186.1781	$186.18	$186.20	$186.20
Purchase #2	$78.48	4.782%	$82.2329	$82.23	$82.25	$82.20
Purchase #3	$161.91	13.654%	$184.0172	$184.02	$184.00	$184.00
Purchase #4	$55.66	11.109%	$61.8433	$61.84	$61.85	$61.80
Purchase #5	$180.29	10.304%	$198.8671	$198.87	$198.85	$198.90
Purchase #6	$37.85	7.654%	$40.747	$40.75	$40.75	$40.70
Purchase #7	$230.32	6.510%	$245.3138	$245.31	$245.30	$245.30
7 purchase totals =	$923.90		$999.1994	$999.20	$999.20	$999.10