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	$137.58	13.542%	$156.2111	$156.21	$156.20	$156.20
Purchase #2	$115.59	7.129%	$123.8304	$123.83	$123.85	$123.80
Purchase #3	$165.52	8.120%	$178.9602	$178.96	$178.95	$179.00
Purchase #4	$189.44	3.713%	$196.4739	$196.47	$196.45	$196.50
Purchase #5	$140.36	7.555%	$150.9642	$150.96	$150.95	$151.00
Purchase #6	$29.78	5.671%	$31.4688	$31.47	$31.45	$31.50
Purchase #7	$37.54	13.546%	$42.6252	$42.63	$42.65	$42.60
7 purchase totals =	$815.81		$880.5338	$880.53	$880.50	$880.60