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	$100.92	8.388%	$109.3852	$109.39	$109.40	$109.40
Purchase #2	$59.68	3.298%	$61.6482	$61.65	$61.65	$61.60
Purchase #3	$27.51	4.841%	$28.8418	$28.84	$28.85	$28.80
Purchase #4	$152.79	6.218%	$162.2905	$162.29	$162.30	$162.30
Purchase #5	$51.85	13.594%	$58.8985	$58.90	$58.90	$58.90
Purchase #6	$129.54	6.788%	$138.3332	$138.33	$138.35	$138.30
Purchase #7	$80.92	10.416%	$89.3486	$89.35	$89.35	$89.30
7 purchase totals =	$603.21		$648.7460	$648.75	$648.80	$648.60