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	$211.56	12.715%	$238.4599	$238.46	$238.45	$238.50
Purchase #2	$65.69	9.302%	$71.8005	$71.80	$71.80	$71.80
Purchase #3	$114.58	13.310%	$129.8306	$129.83	$129.85	$129.80
Purchase #4	$5.65	11.780%	$6.3156	$6.32	$6.30	$6.30
Purchase #5	$104.72	8.820%	$113.9563	$113.96	$113.95	$114.00
Purchase #6	$64.28	4.573%	$67.2195	$67.22	$67.20	$67.20
Purchase #7	$18.90	10.341%	$20.8544	$20.85	$20.85	$20.90
7 purchase totals =	$585.38		$648.4368	$648.44	$648.40	$648.50