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	$55.85	6.402%	$59.4255	$59.43	$59.45	$59.40
Purchase #2	$70.80	4.399%	$73.9145	$73.91	$73.90	$73.90
Purchase #3	$109.79	12.259%	$123.2492	$123.25	$123.25	$123.20
Purchase #4	$28.30	4.547%	$29.5868	$29.59	$29.60	$29.60
Purchase #5	$39.85	5.861%	$42.1856	$42.19	$42.20	$42.20
Purchase #6	$202.85	9.453%	$222.0254	$222.03	$222.05	$222.00
Purchase #7	$217.41	10.783%	$240.8533	$240.85	$240.85	$240.90
7 purchase totals =	$724.85		$791.2403	$791.25	$791.30	$791.20