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	$74.67	11.404%	$83.1854	$83.19	$83.20	$83.20
Purchase #2	$249.67	4.114%	$259.9414	$259.94	$259.95	$259.90
Purchase #3	$197.49	10.874%	$218.9651	$218.97	$218.95	$219.00
Purchase #4	$116.59	13.259%	$132.0487	$132.05	$132.05	$132.00
Purchase #5	$128.81	12.214%	$144.5429	$144.54	$144.55	$144.50
Purchase #6	$150.84	11.772%	$168.5969	$168.60	$168.60	$168.60
Purchase #7	$244.74	4.543%	$255.8585	$255.86	$255.85	$255.90
7 purchase totals =	$1,162.81		$1,263.1389	$1,263.15	$1,263.15	$1,263.10