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	$232.40	4.354%	$242.5187	$242.52	$242.50	$242.50
Purchase #2	$209.96	10.149%	$231.2688	$231.27	$231.25	$231.30
Purchase #3	$140.76	13.810%	$160.199	$160.20	$160.20	$160.20
Purchase #4	$50.30	5.190%	$52.9106	$52.91	$52.90	$52.90
Purchase #5	$120.83	5.340%	$127.2823	$127.28	$127.30	$127.30
Purchase #6	$123.82	9.128%	$135.1223	$135.12	$135.10	$135.10
Purchase #7	$124.91	5.749%	$132.0911	$132.09	$132.10	$132.10
7 purchase totals =	$1,002.98		$1,081.3928	$1,081.39	$1,081.35	$1,081.40