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	$37.66	5.853%	$39.8642	$39.86	$39.85	$39.90
Purchase #2	$175.87	6.570%	$187.4247	$187.42	$187.40	$187.40
Purchase #3	$237.90	4.409%	$248.389	$248.39	$248.40	$248.40
Purchase #4	$220.30	13.528%	$250.1022	$250.10	$250.10	$250.10
Purchase #5	$30.60	11.850%	$34.2261	$34.23	$34.25	$34.20
Purchase #6	$192.45	12.191%	$215.9116	$215.91	$215.90	$215.90
Purchase #7	$137.53	10.603%	$152.1123	$152.11	$152.10	$152.10
7 purchase totals =	$1,032.31		$1,128.0301	$1,128.02	$1,128.00	$1,128.00