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	$61.86	13.672%	$70.3175	$70.32	$70.30	$70.30
Purchase #2	$168.66	9.479%	$184.6473	$184.65	$184.65	$184.60
Purchase #3	$18.77	8.131%	$20.2962	$20.30	$20.30	$20.30
Purchase #4	$27.95	6.256%	$29.6986	$29.70	$29.70	$29.70
Purchase #5	$103.88	5.755%	$109.8583	$109.86	$109.85	$109.90
Purchase #6	$91.36	8.293%	$98.9365	$98.94	$98.95	$98.90
Purchase #7	$78.89	3.759%	$81.8555	$81.86	$81.85	$81.90
7 purchase totals =	$551.37		$595.6099	$595.63	$595.60	$595.60