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	$56.32	12.561%	$63.3944	$63.39	$63.40	$63.40
Purchase #2	$88.29	4.787%	$92.5164	$92.52	$92.50	$92.50
Purchase #3	$21.46	12.844%	$24.2163	$24.22	$24.20	$24.20
Purchase #4	$29.56	12.763%	$33.3327	$33.33	$33.35	$33.30
Purchase #5	$130.90	8.440%	$141.948	$141.95	$141.95	$141.90
Purchase #6	$106.36	3.250%	$109.8167	$109.82	$109.80	$109.80
Purchase #7	$128.63	13.869%	$146.4697	$146.47	$146.45	$146.50
7 purchase totals =	$561.52		$611.6942	$611.70	$611.65	$611.60