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	$25.35	5.854%	$26.834	$26.83	$26.85	$26.80
Purchase #2	$215.97	6.197%	$229.3537	$229.35	$229.35	$229.40
Purchase #3	$70.86	11.430%	$78.9593	$78.96	$78.95	$79.00
Purchase #4	$247.54	13.228%	$280.2846	$280.28	$280.30	$280.30
Purchase #5	$82.65	3.843%	$85.8262	$85.83	$85.85	$85.80
Purchase #6	$143.63	6.228%	$152.5753	$152.58	$152.60	$152.60
Purchase #7	$152.75	10.814%	$169.2684	$169.27	$169.25	$169.30
7 purchase totals =	$938.75		$1,023.1015	$1,023.10	$1,023.15	$1,023.20