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	$81.99	10.445%	$90.5539	$90.55	$90.55	$90.60
Purchase #2	$71.82	9.153%	$78.3937	$78.39	$78.40	$78.40
Purchase #3	$234.63	10.854%	$260.0967	$260.10	$260.10	$260.10
Purchase #4	$75.70	13.709%	$86.0777	$86.08	$86.10	$86.10
Purchase #5	$83.38	11.306%	$92.8069	$92.81	$92.80	$92.80
Purchase #6	$58.29	4.833%	$61.1072	$61.11	$61.10	$61.10
Purchase #7	$96.67	7.416%	$103.839	$103.84	$103.85	$103.80
7 purchase totals =	$702.48		$772.8751	$772.88	$772.90	$772.90