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	$81.54	10.623%	$90.202	$90.20	$90.20	$90.20
Purchase #2	$112.78	9.756%	$123.7828	$123.78	$123.80	$123.80
Purchase #3	$79.89	10.628%	$88.3807	$88.38	$88.40	$88.40
Purchase #4	$143.77	7.636%	$154.7483	$154.75	$154.75	$154.70
Purchase #5	$189.83	11.597%	$211.8446	$211.84	$211.85	$211.80
Purchase #6	$33.67	10.600%	$37.239	$37.24	$37.25	$37.20
Purchase #7	$240.95	9.112%	$262.9054	$262.91	$262.90	$262.90
7 purchase totals =	$882.43		$969.1028	$969.10	$969.15	$969.00