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	$104.75	3.268%	$108.1732	$108.17	$108.15	$108.20
Purchase #2	$63.56	7.146%	$68.102	$68.10	$68.10	$68.10
Purchase #3	$185.92	12.503%	$209.1656	$209.17	$209.15	$209.20
Purchase #4	$199.75	4.768%	$209.2741	$209.27	$209.25	$209.30
Purchase #5	$50.88	7.838%	$54.868	$54.87	$54.85	$54.90
Purchase #6	$33.30	13.805%	$37.8971	$37.90	$37.90	$37.90
Purchase #7	$183.56	3.417%	$189.8322	$189.83	$189.85	$189.80
7 purchase totals =	$821.72		$877.3122	$877.31	$877.25	$877.40