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	$109.27	13.404%	$123.9166	$123.92	$123.90	$123.90
Purchase #2	$5.56	13.603%	$6.3163	$6.32	$6.30	$6.30
Purchase #3	$143.96	12.729%	$162.2847	$162.28	$162.30	$162.30
Purchase #4	$220.98	13.324%	$250.4234	$250.42	$250.40	$250.40
Purchase #5	$142.37	3.649%	$147.5651	$147.57	$147.55	$147.60
Purchase #6	$102.32	4.175%	$106.5919	$106.59	$106.60	$106.60
Purchase #7	$40.30	8.501%	$43.7259	$43.73	$43.75	$43.70
7 purchase totals =	$764.76		$840.8239	$840.83	$840.80	$840.80