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	$147.73	13.786%	$168.0961	$168.10	$168.10	$168.10
Purchase #2	$109.57	3.665%	$113.5857	$113.59	$113.60	$113.60
Purchase #3	$193.77	9.657%	$212.4824	$212.48	$212.50	$212.50
Purchase #4	$168.50	6.458%	$179.3817	$179.38	$179.40	$179.40
Purchase #5	$139.78	13.440%	$158.5664	$158.57	$158.55	$158.60
Purchase #6	$41.94	9.626%	$45.9771	$45.98	$46.00	$46.00
Purchase #7	$234.66	12.348%	$263.6358	$263.64	$263.65	$263.60
7 purchase totals =	$1,035.95		$1,141.7252	$1,141.74	$1,141.80	$1,141.80