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	$66.67	9.321%	$72.8843	$72.88	$72.90	$72.90
Purchase #2	$42.72	6.573%	$45.528	$45.53	$45.55	$45.50
Purchase #3	$116.25	10.481%	$128.4342	$128.43	$128.45	$128.40
Purchase #4	$84.40	10.599%	$93.3456	$93.35	$93.35	$93.30
Purchase #5	$227.89	13.852%	$259.4573	$259.46	$259.45	$259.50
Purchase #6	$85.44	3.300%	$88.2595	$88.26	$88.25	$88.30
Purchase #7	$152.28	8.666%	$165.4766	$165.48	$165.50	$165.50
7 purchase totals =	$775.65		$853.3855	$853.39	$853.45	$853.40