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	$134.54	3.519%	$139.2745	$139.27	$139.25	$139.30
Purchase #2	$105.99	3.702%	$109.9137	$109.91	$109.90	$109.90
Purchase #3	$62.92	12.123%	$70.5478	$70.55	$70.55	$70.50
Purchase #4	$199.72	9.783%	$219.2586	$219.26	$219.25	$219.30
Purchase #5	$172.42	7.125%	$184.7049	$184.70	$184.70	$184.70
Purchase #6	$112.82	9.228%	$123.231	$123.23	$123.25	$123.20
Purchase #7	$240.25	6.242%	$255.2464	$255.25	$255.25	$255.20
7 purchase totals =	$1,028.66		$1,102.1769	$1,102.17	$1,102.15	$1,102.10