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	$180.32	3.643%	$186.8891	$186.89	$186.90	$186.90
Purchase #2	$39.94	13.369%	$45.2796	$45.28	$45.30	$45.30
Purchase #3	$167.93	9.809%	$184.4023	$184.40	$184.40	$184.40
Purchase #4	$230.25	10.459%	$254.3318	$254.33	$254.35	$254.30
Purchase #5	$7.86	6.602%	$8.3789	$8.38	$8.40	$8.40
Purchase #6	$126.45	12.114%	$141.7682	$141.77	$141.75	$141.80
Purchase #7	$82.52	13.409%	$93.5851	$93.59	$93.60	$93.60
7 purchase totals =	$835.27		$914.6350	$914.64	$914.70	$914.70