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	$34.80	7.548%	$37.4267	$37.43	$37.45	$37.40
Purchase #2	$17.50	4.868%	$18.3519	$18.35	$18.35	$18.40
Purchase #3	$47.54	7.503%	$51.1069	$51.11	$51.10	$51.10
Purchase #4	$197.41	9.293%	$215.7553	$215.76	$215.75	$215.80
Purchase #5	$187.47	9.626%	$205.5159	$205.52	$205.50	$205.50
Purchase #6	$86.35	6.152%	$91.6623	$91.66	$91.65	$91.70
Purchase #7	$135.75	10.732%	$150.3187	$150.32	$150.30	$150.30
7 purchase totals =	$706.82		$770.1377	$770.15	$770.10	$770.20