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	$16.33	9.797%	$17.9299	$17.93	$17.95	$17.90
Purchase #2	$249.83	12.778%	$281.7533	$281.75	$281.75	$281.80
Purchase #3	$177.75	7.184%	$190.5196	$190.52	$190.50	$190.50
Purchase #4	$41.88	3.626%	$43.3986	$43.40	$43.40	$43.40
Purchase #5	$34.84	6.152%	$36.9834	$36.98	$37.00	$37.00
Purchase #6	$220.36	13.840%	$250.8578	$250.86	$250.85	$250.90
Purchase #7	$162.88	11.376%	$181.4092	$181.41	$181.40	$181.40
7 purchase totals =	$903.87		$1,002.8518	$1,002.85	$1,002.85	$1,002.90