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	$122.32	7.173%	$131.094	$131.09	$131.10	$131.10
Purchase #2	$235.32	7.332%	$252.5737	$252.57	$252.55	$252.60
Purchase #3	$157.32	13.803%	$179.0349	$179.03	$179.05	$179.00
Purchase #4	$50.70	7.489%	$54.4969	$54.50	$54.50	$54.50
Purchase #5	$115.43	13.824%	$131.387	$131.39	$131.40	$131.40
Purchase #6	$173.30	4.773%	$181.5716	$181.57	$181.55	$181.60
Purchase #7	$36.32	9.802%	$39.8801	$39.88	$39.90	$39.90
7 purchase totals =	$890.71		$970.0382	$970.03	$970.05	$970.10