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	$195.42	7.219%	$209.5274	$209.53	$209.55	$209.50
Purchase #2	$226.95	6.139%	$240.8825	$240.88	$240.90	$240.90
Purchase #3	$29.80	10.123%	$32.8167	$32.82	$32.80	$32.80
Purchase #4	$237.30	5.577%	$250.5342	$250.53	$250.55	$250.50
Purchase #5	$70.61	4.867%	$74.0466	$74.05	$74.05	$74.00
Purchase #6	$130.86	9.183%	$142.8769	$142.88	$142.90	$142.90
Purchase #7	$99.64	9.574%	$109.1795	$109.18	$109.20	$109.20
7 purchase totals =	$990.58		$1,059.8638	$1,059.87	$1,059.95	$1,059.80