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	$63.47	3.666%	$65.7968	$65.80	$65.80	$65.80
Purchase #2	$60.75	9.441%	$66.4854	$66.49	$66.50	$66.50
Purchase #3	$120.81	3.547%	$125.0951	$125.10	$125.10	$125.10
Purchase #4	$95.43	9.524%	$104.5188	$104.52	$104.50	$104.50
Purchase #5	$54.89	8.259%	$59.4234	$59.42	$59.40	$59.40
Purchase #6	$18.58	13.214%	$21.0352	$21.04	$21.05	$21.00
Purchase #7	$236.54	11.560%	$263.884	$263.88	$263.90	$263.90
7 purchase totals =	$650.47		$706.2387	$706.25	$706.25	$706.20