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	$26.56	6.685%	$28.3355	$28.34	$28.35	$28.30
Purchase #2	$180.25	11.475%	$200.9337	$200.93	$200.95	$200.90
Purchase #3	$229.83	4.190%	$239.4599	$239.46	$239.45	$239.50
Purchase #4	$13.76	11.764%	$15.3787	$15.38	$15.40	$15.40
Purchase #5	$45.48	12.734%	$51.2714	$51.27	$51.25	$51.30
Purchase #6	$227.87	5.723%	$240.911	$240.91	$240.90	$240.90
Purchase #7	$176.60	13.616%	$200.6459	$200.65	$200.65	$200.60
7 purchase totals =	$900.35		$976.9361	$976.94	$976.95	$976.90