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	$18.77	10.645%	$20.7681	$20.77	$20.75	$20.80
Purchase #2	$56.48	9.519%	$61.8563	$61.86	$61.85	$61.90
Purchase #3	$165.71	4.264%	$172.7759	$172.78	$172.80	$172.80
Purchase #4	$36.52	13.464%	$41.4371	$41.44	$41.45	$41.40
Purchase #5	$24.63	10.641%	$27.2509	$27.25	$27.25	$27.30
Purchase #6	$78.59	5.201%	$82.6775	$82.68	$82.70	$82.70
Purchase #7	$248.72	12.467%	$279.7279	$279.73	$279.75	$279.70
7 purchase totals =	$629.42		$686.4937	$686.51	$686.55	$686.60