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	$27.43	13.210%	$31.0535	$31.05	$31.05	$31.10
Purchase #2	$165.98	13.215%	$187.9143	$187.91	$187.90	$187.90
Purchase #3	$206.58	13.477%	$234.4208	$234.42	$234.40	$234.40
Purchase #4	$138.30	9.554%	$151.5132	$151.51	$151.50	$151.50
Purchase #5	$48.40	12.379%	$54.3914	$54.39	$54.40	$54.40
Purchase #6	$169.80	13.560%	$192.8249	$192.82	$192.80	$192.80
Purchase #7	$186.51	6.799%	$199.1908	$199.19	$199.20	$199.20
7 purchase totals =	$943.00		$1,051.3089	$1,051.29	$1,051.25	$1,051.30