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	$36.75	10.458%	$40.5933	$40.59	$40.60	$40.60
Purchase #2	$250.98	11.111%	$278.8664	$278.87	$278.85	$278.90
Purchase #3	$188.41	12.536%	$212.0291	$212.03	$212.05	$212.00
Purchase #4	$196.54	11.634%	$219.4055	$219.41	$219.40	$219.40
Purchase #5	$86.85	13.399%	$98.487	$98.49	$98.50	$98.50
Purchase #6	$242.44	9.510%	$265.496	$265.50	$265.50	$265.50
Purchase #7	$166.25	9.578%	$182.1734	$182.17	$182.15	$182.20
7 purchase totals =	$1,168.22		$1,297.0507	$1,297.06	$1,297.05	$1,297.10