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	$100.88	12.478%	$113.4678	$113.47	$113.45	$113.50
Purchase #2	$180.49	8.122%	$195.1494	$195.15	$195.15	$195.10
Purchase #3	$174.43	12.818%	$196.7884	$196.79	$196.80	$196.80
Purchase #4	$127.94	5.198%	$134.5903	$134.59	$134.60	$134.60
Purchase #5	$180.44	5.597%	$190.5392	$190.54	$190.55	$190.50
Purchase #6	$113.72	9.288%	$124.2823	$124.28	$124.30	$124.30
Purchase #7	$129.64	5.731%	$137.0697	$137.07	$137.05	$137.10
7 purchase totals =	$1,007.54		$1,091.8871	$1,091.89	$1,091.90	$1,091.90