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	$115.93	13.446%	$131.5179	$131.52	$131.50	$131.50
Purchase #2	$65.33	3.329%	$67.5048	$67.50	$67.50	$67.50
Purchase #3	$44.82	7.583%	$48.2187	$48.22	$48.20	$48.20
Purchase #4	$54.51	12.848%	$61.5134	$61.51	$61.50	$61.50
Purchase #5	$86.37	11.568%	$96.3613	$96.36	$96.35	$96.40
Purchase #6	$36.55	11.777%	$40.8545	$40.85	$40.85	$40.90
Purchase #7	$231.28	8.784%	$251.5956	$251.60	$251.60	$251.60
7 purchase totals =	$634.79		$697.5662	$697.56	$697.50	$697.60