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	$71.88	13.401%	$81.5126	$81.51	$81.50	$81.50
Purchase #2	$171.74	4.617%	$179.6692	$179.67	$179.65	$179.70
Purchase #3	$240.25	6.463%	$255.7774	$255.78	$255.80	$255.80
Purchase #4	$29.50	8.206%	$31.9208	$31.92	$31.90	$31.90
Purchase #5	$110.35	5.581%	$116.5086	$116.51	$116.50	$116.50
Purchase #6	$249.51	10.305%	$275.222	$275.22	$275.20	$275.20
Purchase #7	$188.45	12.220%	$211.4786	$211.48	$211.50	$211.50
7 purchase totals =	$1,061.68		$1,152.0892	$1,152.09	$1,152.05	$1,152.10