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	$250.33	7.842%	$269.9609	$269.96	$269.95	$270.00
Purchase #2	$243.34	3.699%	$252.3411	$252.34	$252.35	$252.30
Purchase #3	$74.99	6.546%	$79.8988	$79.90	$79.90	$79.90
Purchase #4	$85.37	6.439%	$90.867	$90.87	$90.85	$90.90
Purchase #5	$80.46	9.846%	$88.3821	$88.38	$88.40	$88.40
Purchase #6	$238.47	4.351%	$248.8458	$248.85	$248.85	$248.80
Purchase #7	$58.82	13.112%	$66.5325	$66.53	$66.55	$66.50
7 purchase totals =	$1,031.78		$1,096.8282	$1,096.83	$1,096.85	$1,096.80