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	$80.84	11.549%	$90.1762	$90.18	$90.20	$90.20
Purchase #2	$54.82	4.597%	$57.3401	$57.34	$57.35	$57.30
Purchase #3	$121.64	6.469%	$129.5089	$129.51	$129.50	$129.50
Purchase #4	$43.26	8.316%	$46.8575	$46.86	$46.85	$46.90
Purchase #5	$224.51	11.411%	$250.1288	$250.13	$250.15	$250.10
Purchase #6	$65.90	10.647%	$72.9164	$72.92	$72.90	$72.90
Purchase #7	$78.60	6.445%	$83.6658	$83.67	$83.65	$83.70
7 purchase totals =	$669.57		$730.5937	$730.61	$730.60	$730.60