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	$181.30	5.293%	$190.8962	$190.90	$190.90	$190.90
Purchase #2	$100.42	4.740%	$105.1799	$105.18	$105.20	$105.20
Purchase #3	$100.86	4.824%	$105.7255	$105.73	$105.75	$105.70
Purchase #4	$82.66	11.238%	$91.9493	$91.95	$91.95	$91.90
Purchase #5	$116.37	8.773%	$126.5791	$126.58	$126.60	$126.60
Purchase #6	$26.46	5.731%	$27.9764	$27.98	$28.00	$28.00
Purchase #7	$116.39	4.730%	$121.8952	$121.90	$121.90	$121.90
7 purchase totals =	$724.46		$770.2016	$770.22	$770.30	$770.20