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	$78.47	5.399%	$82.7066	$82.71	$82.70	$82.70
Purchase #2	$32.97	13.234%	$37.3332	$37.33	$37.35	$37.30
Purchase #3	$232.72	9.762%	$255.4381	$255.44	$255.45	$255.40
Purchase #4	$129.57	13.357%	$146.8767	$146.88	$146.90	$146.90
Purchase #5	$240.38	3.686%	$249.2404	$249.24	$249.25	$249.20
Purchase #6	$18.95	13.149%	$21.4417	$21.44	$21.45	$21.40
Purchase #7	$146.28	12.650%	$164.7844	$164.78	$164.80	$164.80
7 purchase totals =	$879.34		$957.8211	$957.82	$957.90	$957.70