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	$229.76	13.628%	$261.0717	$261.07	$261.05	$261.10
Purchase #2	$108.54	13.567%	$123.2656	$123.27	$123.25	$123.30
Purchase #3	$44.63	11.481%	$49.754	$49.75	$49.75	$49.80
Purchase #4	$82.32	12.668%	$92.7483	$92.75	$92.75	$92.70
Purchase #5	$83.69	7.731%	$90.1601	$90.16	$90.15	$90.20
Purchase #6	$180.90	10.183%	$199.321	$199.32	$199.30	$199.30
Purchase #7	$25.55	10.372%	$28.2	$28.20	$28.20	$28.20
7 purchase totals =	$755.39		$844.5207	$844.52	$844.45	$844.60