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	$232.70	7.697%	$250.6109	$250.61	$250.60	$250.60
Purchase #2	$131.39	10.221%	$144.8194	$144.82	$144.80	$144.80
Purchase #3	$47.52	11.113%	$52.8009	$52.80	$52.80	$52.80
Purchase #4	$220.41	11.448%	$245.6425	$245.64	$245.65	$245.60
Purchase #5	$41.48	13.316%	$47.0035	$47.00	$47.00	$47.00
Purchase #6	$20.89	3.456%	$21.612	$21.61	$21.60	$21.60
Purchase #7	$191.32	9.117%	$208.7626	$208.76	$208.75	$208.80
7 purchase totals =	$885.71		$971.2518	$971.24	$971.20	$971.20