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	$19.63	6.530%	$20.9118	$20.91	$20.90	$20.90
Purchase #2	$60.64	9.836%	$66.6046	$66.60	$66.60	$66.60
Purchase #3	$95.57	12.772%	$107.7762	$107.78	$107.80	$107.80
Purchase #4	$78.33	6.868%	$83.7097	$83.71	$83.70	$83.70
Purchase #5	$34.94	9.410%	$38.2279	$38.23	$38.25	$38.20
Purchase #6	$134.91	12.611%	$151.9235	$151.92	$151.90	$151.90
Purchase #7	$218.59	11.224%	$243.1245	$243.12	$243.10	$243.10
7 purchase totals =	$642.61		$712.2782	$712.27	$712.25	$712.20