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	$30.26	4.745%	$31.6958	$31.70	$31.70	$31.70
Purchase #2	$113.89	12.771%	$128.4349	$128.43	$128.45	$128.40
Purchase #3	$49.87	9.568%	$54.6416	$54.64	$54.65	$54.60
Purchase #4	$29.86	10.821%	$33.0912	$33.09	$33.10	$33.10
Purchase #5	$78.30	4.874%	$82.1163	$82.12	$82.10	$82.10
Purchase #6	$160.88	12.572%	$181.1058	$181.11	$181.10	$181.10
Purchase #7	$74.66	8.206%	$80.7866	$80.79	$80.80	$80.80
7 purchase totals =	$537.72		$591.8722	$591.88	$591.90	$591.80