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	$115.34	12.136%	$129.3377	$129.34	$129.35	$129.30
Purchase #2	$221.39	9.296%	$241.9704	$241.97	$241.95	$242.00
Purchase #3	$242.28	10.333%	$267.3148	$267.31	$267.30	$267.30
Purchase #4	$115.38	7.236%	$123.7289	$123.73	$123.75	$123.70
Purchase #5	$34.30	9.219%	$37.4621	$37.46	$37.45	$37.50
Purchase #6	$6.31	13.256%	$7.1465	$7.15	$7.15	$7.10
Purchase #7	$156.69	6.137%	$166.3061	$166.31	$166.30	$166.30
7 purchase totals =	$891.69		$973.2665	$973.27	$973.25	$973.20