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	$73.89	11.494%	$82.3829	$82.38	$82.40	$82.40
Purchase #2	$250.27	11.787%	$279.7693	$279.77	$279.75	$279.80
Purchase #3	$127.73	13.299%	$144.7168	$144.72	$144.70	$144.70
Purchase #4	$74.72	10.554%	$82.6059	$82.61	$82.60	$82.60
Purchase #5	$124.86	4.257%	$130.1753	$130.18	$130.20	$130.20
Purchase #6	$108.34	13.416%	$122.8749	$122.87	$122.85	$122.90
Purchase #7	$79.50	11.703%	$88.8039	$88.80	$88.80	$88.80
7 purchase totals =	$839.31		$931.3290	$931.33	$931.30	$931.40