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	$14.32	12.461%	$16.1044	$16.10	$16.10	$16.10
Purchase #2	$82.48	4.732%	$86.383	$86.38	$86.40	$86.40
Purchase #3	$245.54	10.141%	$270.4402	$270.44	$270.45	$270.40
Purchase #4	$172.94	9.683%	$189.6858	$189.69	$189.70	$189.70
Purchase #5	$35.60	9.197%	$38.8741	$38.87	$38.85	$38.90
Purchase #6	$52.49	13.363%	$59.5042	$59.50	$59.50	$59.50
Purchase #7	$39.97	13.226%	$45.2564	$45.26	$45.25	$45.30
7 purchase totals =	$643.34		$706.2481	$706.24	$706.25	$706.30