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	$202.90	9.592%	$222.3622	$222.36	$222.35	$222.40
Purchase #2	$82.93	6.841%	$88.6032	$88.60	$88.60	$88.60
Purchase #3	$29.45	7.770%	$31.7383	$31.74	$31.75	$31.70
Purchase #4	$90.86	9.629%	$99.6089	$99.61	$99.60	$99.60
Purchase #5	$132.31	5.809%	$139.9959	$140.00	$140.00	$140.00
Purchase #6	$19.72	6.412%	$20.9844	$20.98	$21.00	$21.00
Purchase #7	$30.50	9.470%	$33.3884	$33.39	$33.40	$33.40
7 purchase totals =	$588.67		$636.6813	$636.68	$636.70	$636.70