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	$222.52	6.650%	$237.3176	$237.32	$237.30	$237.30
Purchase #2	$105.39	9.441%	$115.3399	$115.34	$115.35	$115.30
Purchase #3	$217.85	7.785%	$234.8096	$234.81	$234.80	$234.80
Purchase #4	$180.27	8.152%	$194.9656	$194.97	$194.95	$195.00
Purchase #5	$71.83	9.496%	$78.651	$78.65	$78.65	$78.70
Purchase #6	$18.37	10.607%	$20.3185	$20.32	$20.30	$20.30
Purchase #7	$120.68	12.296%	$135.5188	$135.52	$135.50	$135.50
7 purchase totals =	$936.91		$1,016.9210	$1,016.93	$1,016.85	$1,016.90