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	$123.36	13.324%	$139.7965	$139.80	$139.80	$139.80
Purchase #2	$218.55	11.150%	$242.9183	$242.92	$242.90	$242.90
Purchase #3	$107.31	8.549%	$116.4839	$116.48	$116.50	$116.50
Purchase #4	$129.56	7.703%	$139.54	$139.54	$139.55	$139.50
Purchase #5	$159.85	13.279%	$181.0765	$181.08	$181.10	$181.10
Purchase #6	$123.37	6.416%	$131.2854	$131.29	$131.30	$131.30
Purchase #7	$101.45	7.355%	$108.9116	$108.91	$108.90	$108.90
7 purchase totals =	$963.45		$1,060.0122	$1,060.02	$1,060.05	$1,060.00