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	$126.66	10.369%	$139.7934	$139.79	$139.80	$139.80
Purchase #2	$171.25	6.809%	$182.9104	$182.91	$182.90	$182.90
Purchase #3	$72.28	13.371%	$81.9446	$81.94	$81.95	$81.90
Purchase #4	$152.68	13.552%	$173.3712	$173.37	$173.35	$173.40
Purchase #5	$224.92	8.647%	$244.3688	$244.37	$244.35	$244.40
Purchase #6	$65.77	10.366%	$72.5877	$72.59	$72.60	$72.60
Purchase #7	$73.81	8.837%	$80.3326	$80.33	$80.35	$80.30
7 purchase totals =	$887.37		$975.3087	$975.30	$975.30	$975.30