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	$190.88	13.839%	$217.2959	$217.30	$217.30	$217.30
Purchase #2	$54.66	9.430%	$59.8144	$59.81	$59.80	$59.80
Purchase #3	$19.32	9.308%	$21.1183	$21.12	$21.10	$21.10
Purchase #4	$232.77	3.548%	$241.0287	$241.03	$241.05	$241.00
Purchase #5	$231.75	3.794%	$240.5426	$240.54	$240.55	$240.50
Purchase #6	$70.76	11.486%	$78.8875	$78.89	$78.90	$78.90
Purchase #7	$66.78	3.657%	$69.2221	$69.22	$69.20	$69.20
7 purchase totals =	$866.92		$927.9095	$927.91	$927.90	$927.80