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	$81.81	10.172%	$90.1317	$90.13	$90.15	$90.10
Purchase #2	$187.35	4.296%	$195.3986	$195.40	$195.40	$195.40
Purchase #3	$106.73	9.488%	$116.8565	$116.86	$116.85	$116.90
Purchase #4	$246.64	13.842%	$280.7799	$280.78	$280.80	$280.80
Purchase #5	$96.98	10.279%	$106.9486	$106.95	$106.95	$106.90
Purchase #6	$225.98	4.398%	$235.9186	$235.92	$235.90	$235.90
Purchase #7	$243.89	7.534%	$262.2647	$262.26	$262.25	$262.30
7 purchase totals =	$1,189.38		$1,288.2986	$1,288.30	$1,288.30	$1,288.30