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	$105.98	3.343%	$109.5229	$109.52	$109.50	$109.50
Purchase #2	$19.28	13.277%	$21.8398	$21.84	$21.85	$21.80
Purchase #3	$87.56	6.219%	$93.0054	$93.01	$93.00	$93.00
Purchase #4	$55.92	12.461%	$62.8882	$62.89	$62.90	$62.90
Purchase #5	$70.98	10.834%	$78.67	$78.67	$78.65	$78.70
Purchase #6	$71.84	13.378%	$81.4508	$81.45	$81.45	$81.50
Purchase #7	$104.89	3.265%	$108.3147	$108.31	$108.30	$108.30
7 purchase totals =	$516.45		$555.6918	$555.69	$555.65	$555.70