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	$86.60	5.219%	$91.1197	$91.12	$91.10	$91.10
Purchase #2	$57.43	4.360%	$59.9339	$59.93	$59.95	$59.90
Purchase #3	$176.72	6.385%	$188.0036	$188.00	$188.00	$188.00
Purchase #4	$116.46	5.485%	$122.8478	$122.85	$122.85	$122.80
Purchase #5	$203.61	7.122%	$218.1111	$218.11	$218.10	$218.10
Purchase #6	$90.43	5.378%	$95.2933	$95.29	$95.30	$95.30
Purchase #7	$10.36	11.318%	$11.5325	$11.53	$11.55	$11.50
7 purchase totals =	$741.61		$786.8419	$786.83	$786.85	$786.70