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	$66.44	5.219%	$69.9075	$69.91	$69.90	$69.90
Purchase #2	$59.42	8.277%	$64.3382	$64.34	$64.35	$64.30
Purchase #3	$65.93	7.668%	$70.9855	$70.99	$71.00	$71.00
Purchase #4	$110.98	11.163%	$123.3687	$123.37	$123.35	$123.40
Purchase #5	$85.61	4.492%	$89.4556	$89.46	$89.45	$89.50
Purchase #6	$175.73	10.674%	$194.4874	$194.49	$194.50	$194.50
Purchase #7	$233.83	5.398%	$246.4521	$246.45	$246.45	$246.50
7 purchase totals =	$797.94		$858.9950	$859.01	$859.00	$859.10