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	$27.97	4.541%	$29.2401	$29.24	$29.25	$29.20
Purchase #2	$239.39	5.688%	$253.0065	$253.01	$253.00	$253.00
Purchase #3	$53.33	13.392%	$60.472	$60.47	$60.45	$60.50
Purchase #4	$54.41	10.137%	$59.9255	$59.93	$59.95	$59.90
Purchase #5	$59.31	3.614%	$61.4535	$61.45	$61.45	$61.50
Purchase #6	$232.29	10.244%	$256.0858	$256.09	$256.10	$256.10
Purchase #7	$89.84	11.179%	$99.8832	$99.88	$99.90	$99.90
7 purchase totals =	$756.54		$820.0666	$820.07	$820.10	$820.10