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	$194.76	12.544%	$219.1907	$219.19	$219.20	$219.20
Purchase #2	$129.72	10.142%	$142.8762	$142.88	$142.90	$142.90
Purchase #3	$74.96	6.602%	$79.9089	$79.91	$79.90	$79.90
Purchase #4	$227.63	12.375%	$255.7992	$255.80	$255.80	$255.80
Purchase #5	$59.61	3.787%	$61.8674	$61.87	$61.85	$61.90
Purchase #6	$50.49	7.443%	$54.248	$54.25	$54.25	$54.20
Purchase #7	$86.39	3.540%	$89.4482	$89.45	$89.45	$89.40
7 purchase totals =	$823.56		$903.3386	$903.35	$903.35	$903.30