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	$54.67	9.462%	$59.8429	$59.84	$59.85	$59.80
Purchase #2	$102.57	13.550%	$116.4682	$116.47	$116.45	$116.50
Purchase #3	$197.90	13.304%	$224.2286	$224.23	$224.25	$224.20
Purchase #4	$23.79	3.780%	$24.6893	$24.69	$24.70	$24.70
Purchase #5	$213.44	12.150%	$239.373	$239.37	$239.35	$239.40
Purchase #6	$188.41	13.752%	$214.3201	$214.32	$214.30	$214.30
Purchase #7	$130.76	7.383%	$140.414	$140.41	$140.40	$140.40
7 purchase totals =	$911.54		$1,019.3361	$1,019.33	$1,019.30	$1,019.30