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	$54.26	4.843%	$56.8878	$56.89	$56.90	$56.90
Purchase #2	$58.75	10.277%	$64.7877	$64.79	$64.80	$64.80
Purchase #3	$198.30	13.417%	$224.9059	$224.91	$224.90	$224.90
Purchase #4	$67.79	6.606%	$72.2682	$72.27	$72.25	$72.30
Purchase #5	$24.57	12.367%	$27.6086	$27.61	$27.60	$27.60
Purchase #6	$113.42	7.494%	$121.9197	$121.92	$121.90	$121.90
Purchase #7	$131.88	9.746%	$144.733	$144.73	$144.75	$144.70
7 purchase totals =	$648.97		$713.1109	$713.12	$713.10	$713.10