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	$141.71	11.781%	$158.4049	$158.40	$158.40	$158.40
Purchase #2	$43.27	7.545%	$46.5347	$46.53	$46.55	$46.50
Purchase #3	$133.33	8.130%	$144.1697	$144.17	$144.15	$144.20
Purchase #4	$126.37	8.529%	$137.1481	$137.15	$137.15	$137.10
Purchase #5	$34.56	13.800%	$39.3293	$39.33	$39.35	$39.30
Purchase #6	$162.26	7.784%	$174.8903	$174.89	$174.90	$174.90
Purchase #7	$240.33	6.310%	$255.4948	$255.49	$255.50	$255.50
7 purchase totals =	$881.83		$955.9718	$955.96	$956.00	$955.90