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	$9.31	5.447%	$9.8171	$9.82	$9.80	$9.80
Purchase #2	$127.57	9.185%	$139.2873	$139.29	$139.30	$139.30
Purchase #3	$162.80	3.708%	$168.8366	$168.84	$168.85	$168.80
Purchase #4	$185.52	3.302%	$191.6459	$191.65	$191.65	$191.60
Purchase #5	$124.65	5.788%	$131.8647	$131.86	$131.85	$131.90
Purchase #6	$19.98	9.644%	$21.9069	$21.91	$21.90	$21.90
Purchase #7	$176.75	7.779%	$190.4994	$190.50	$190.50	$190.50
7 purchase totals =	$806.58		$853.8579	$853.87	$853.85	$853.80