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	$41.52	4.513%	$43.3938	$43.39	$43.40	$43.40
Purchase #2	$250.47	6.825%	$267.5646	$267.56	$267.55	$267.60
Purchase #3	$56.42	5.139%	$59.3194	$59.32	$59.30	$59.30
Purchase #4	$224.89	11.557%	$250.8805	$250.88	$250.90	$250.90
Purchase #5	$157.62	10.355%	$173.9416	$173.94	$173.95	$173.90
Purchase #6	$6.87	5.453%	$7.2446	$7.24	$7.25	$7.20
Purchase #7	$82.89	11.343%	$92.2922	$92.29	$92.30	$92.30
7 purchase totals =	$820.68		$894.6367	$894.62	$894.65	$894.60