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	$138.91	5.318%	$146.2972	$146.30	$146.30	$146.30
Purchase #2	$155.92	10.253%	$171.9065	$171.91	$171.90	$171.90
Purchase #3	$107.36	9.643%	$117.7127	$117.71	$117.70	$117.70
Purchase #4	$80.31	6.406%	$85.4547	$85.45	$85.45	$85.50
Purchase #5	$47.52	8.661%	$51.6357	$51.64	$51.65	$51.60
Purchase #6	$222.89	12.471%	$250.6866	$250.69	$250.70	$250.70
Purchase #7	$152.29	5.571%	$160.7741	$160.77	$160.75	$160.80
7 purchase totals =	$905.20		$984.4675	$984.47	$984.45	$984.50