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	$47.74	7.717%	$51.4241	$51.42	$51.40	$51.40
Purchase #2	$40.54	6.312%	$43.0989	$43.10	$43.10	$43.10
Purchase #3	$167.82	3.258%	$173.2876	$173.29	$173.30	$173.30
Purchase #4	$218.65	9.244%	$238.862	$238.86	$238.85	$238.90
Purchase #5	$189.38	5.333%	$199.4796	$199.48	$199.50	$199.50
Purchase #6	$24.86	12.822%	$28.0475	$28.05	$28.05	$28.00
Purchase #7	$55.78	3.327%	$57.6358	$57.64	$57.65	$57.60
7 purchase totals =	$744.77		$791.8355	$791.84	$791.85	$791.80