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	$42.35	8.454%	$45.9303	$45.93	$45.95	$45.90
Purchase #2	$86.77	3.213%	$89.5579	$89.56	$89.55	$89.60
Purchase #3	$209.81	13.359%	$237.8385	$237.84	$237.85	$237.80
Purchase #4	$36.86	7.157%	$39.4981	$39.50	$39.50	$39.50
Purchase #5	$165.78	10.301%	$182.857	$182.86	$182.85	$182.90
Purchase #6	$23.95	7.275%	$25.6924	$25.69	$25.70	$25.70
Purchase #7	$41.95	3.335%	$43.349	$43.35	$43.35	$43.30
7 purchase totals =	$607.47		$664.7232	$664.73	$664.75	$664.70