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	$20.31	4.809%	$21.2867	$21.29	$21.30	$21.30
Purchase #2	$197.51	6.117%	$209.5917	$209.59	$209.60	$209.60
Purchase #3	$190.61	6.606%	$203.2017	$203.20	$203.20	$203.20
Purchase #4	$119.58	9.209%	$130.5921	$130.59	$130.60	$130.60
Purchase #5	$212.42	4.591%	$222.1722	$222.17	$222.15	$222.20
Purchase #6	$167.92	10.359%	$185.3148	$185.31	$185.30	$185.30
Purchase #7	$181.72	3.850%	$188.7162	$188.72	$188.70	$188.70
7 purchase totals =	$1,090.07		$1,160.8754	$1,160.87	$1,160.85	$1,160.90