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	$190.27	4.793%	$199.3896	$199.39	$199.40	$199.40
Purchase #2	$70.54	12.573%	$79.409	$79.41	$79.40	$79.40
Purchase #3	$146.70	8.540%	$159.2282	$159.23	$159.25	$159.20
Purchase #4	$145.96	4.357%	$152.3195	$152.32	$152.30	$152.30
Purchase #5	$204.44	9.360%	$223.5756	$223.58	$223.60	$223.60
Purchase #6	$93.60	10.647%	$103.5656	$103.57	$103.55	$103.60
Purchase #7	$238.38	13.271%	$270.0154	$270.02	$270.00	$270.00
7 purchase totals =	$1,089.89		$1,187.5029	$1,187.52	$1,187.50	$1,187.50