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	$83.75	7.320%	$89.8805	$89.88	$89.90	$89.90
Purchase #2	$216.27	3.862%	$224.6223	$224.62	$224.60	$224.60
Purchase #3	$112.94	6.485%	$120.2642	$120.26	$120.25	$120.30
Purchase #4	$81.89	5.443%	$86.3473	$86.35	$86.35	$86.30
Purchase #5	$232.50	12.433%	$261.4067	$261.41	$261.40	$261.40
Purchase #6	$210.94	5.346%	$222.2169	$222.22	$222.20	$222.20
Purchase #7	$132.36	12.304%	$148.6456	$148.65	$148.65	$148.60
7 purchase totals =	$1,070.65		$1,153.3835	$1,153.39	$1,153.35	$1,153.30