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	$114.71	11.505%	$127.9074	$127.91	$127.90	$127.90
Purchase #2	$103.41	10.579%	$114.3497	$114.35	$114.35	$114.30
Purchase #3	$219.26	12.296%	$246.2202	$246.22	$246.20	$246.20
Purchase #4	$212.52	4.628%	$222.3554	$222.36	$222.35	$222.40
Purchase #5	$182.56	9.794%	$200.4399	$200.44	$200.45	$200.40
Purchase #6	$44.27	9.869%	$48.639	$48.64	$48.65	$48.60
Purchase #7	$37.74	4.620%	$39.4836	$39.48	$39.50	$39.50
7 purchase totals =	$914.47		$999.3952	$999.40	$999.40	$999.30