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	$55.43	7.446%	$59.5573	$59.56	$59.55	$59.60
Purchase #2	$179.64	5.521%	$189.5579	$189.56	$189.55	$189.60
Purchase #3	$66.49	9.507%	$72.8112	$72.81	$72.80	$72.80
Purchase #4	$246.85	12.130%	$276.7929	$276.79	$276.80	$276.80
Purchase #5	$62.99	12.327%	$70.7548	$70.75	$70.75	$70.80
Purchase #6	$245.44	12.237%	$275.4745	$275.47	$275.45	$275.50
Purchase #7	$143.41	6.315%	$152.4663	$152.47	$152.45	$152.50
7 purchase totals =	$1,000.25		$1,097.4149	$1,097.41	$1,097.35	$1,097.60