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	$247.37	7.314%	$265.4626	$265.46	$265.45	$265.50
Purchase #2	$211.61	12.371%	$237.7883	$237.79	$237.80	$237.80
Purchase #3	$152.62	11.804%	$170.6353	$170.64	$170.65	$170.60
Purchase #4	$151.31	13.546%	$171.8065	$171.81	$171.80	$171.80
Purchase #5	$69.56	10.178%	$76.6398	$76.64	$76.65	$76.60
Purchase #6	$82.31	11.660%	$91.9073	$91.91	$91.90	$91.90
Purchase #7	$134.74	12.854%	$152.0595	$152.06	$152.05	$152.10
7 purchase totals =	$1,049.52		$1,166.2993	$1,166.31	$1,166.30	$1,166.30