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	$174.40	7.451%	$187.3945	$187.39	$187.40	$187.40
Purchase #2	$86.28	13.288%	$97.7449	$97.74	$97.75	$97.70
Purchase #3	$241.58	9.868%	$265.4191	$265.42	$265.40	$265.40
Purchase #4	$33.94	10.326%	$37.4446	$37.44	$37.45	$37.40
Purchase #5	$250.64	11.410%	$279.238	$279.24	$279.25	$279.20
Purchase #6	$139.59	13.108%	$157.8875	$157.89	$157.90	$157.90
Purchase #7	$94.39	8.446%	$102.3622	$102.36	$102.35	$102.40
7 purchase totals =	$1,020.82		$1,127.4908	$1,127.48	$1,127.50	$1,127.40