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	$32.32	5.725%	$34.1703	$34.17	$34.15	$34.20
Purchase #2	$62.41	5.107%	$65.5973	$65.60	$65.60	$65.60
Purchase #3	$109.55	4.317%	$114.2793	$114.28	$114.30	$114.30
Purchase #4	$55.72	6.575%	$59.3836	$59.38	$59.40	$59.40
Purchase #5	$96.81	7.338%	$103.9139	$103.91	$103.90	$103.90
Purchase #6	$72.64	3.782%	$75.3872	$75.39	$75.40	$75.40
Purchase #7	$144.46	3.404%	$149.3774	$149.38	$149.40	$149.40
7 purchase totals =	$573.91		$602.1090	$602.11	$602.15	$602.20