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	$27.66	12.867%	$31.219	$31.22	$31.20	$31.20
Purchase #2	$241.56	6.128%	$256.3628	$256.36	$256.35	$256.40
Purchase #3	$225.89	8.864%	$245.9129	$245.91	$245.90	$245.90
Purchase #4	$25.70	13.198%	$29.0919	$29.09	$29.10	$29.10
Purchase #5	$248.61	11.269%	$276.6259	$276.63	$276.65	$276.60
Purchase #6	$94.53	7.546%	$101.6632	$101.66	$101.65	$101.70
Purchase #7	$71.49	9.673%	$78.4052	$78.41	$78.40	$78.40
7 purchase totals =	$935.44		$1,019.2809	$1,019.28	$1,019.25	$1,019.30