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	$38.97	11.607%	$43.4932	$43.49	$43.50	$43.50
Purchase #2	$30.26	7.351%	$32.4844	$32.48	$32.50	$32.50
Purchase #3	$47.90	11.179%	$53.2547	$53.25	$53.25	$53.30
Purchase #4	$82.43	4.612%	$86.2317	$86.23	$86.25	$86.20
Purchase #5	$143.72	5.265%	$151.2869	$151.29	$151.30	$151.30
Purchase #6	$165.41	5.810%	$175.0203	$175.02	$175.00	$175.00
Purchase #7	$213.89	11.641%	$238.7889	$238.79	$238.80	$238.80
7 purchase totals =	$722.58		$780.5601	$780.55	$780.60	$780.60