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	$88.65	13.294%	$100.4351	$100.44	$100.45	$100.40
Purchase #2	$63.96	5.670%	$67.5865	$67.59	$67.60	$67.60
Purchase #3	$194.89	10.625%	$215.5971	$215.60	$215.60	$215.60
Purchase #4	$164.60	8.409%	$178.4412	$178.44	$178.45	$178.40
Purchase #5	$166.46	3.524%	$172.3261	$172.33	$172.35	$172.30
Purchase #6	$249.52	10.153%	$274.8538	$274.85	$274.85	$274.90
Purchase #7	$92.35	7.131%	$98.9355	$98.94	$98.95	$98.90
7 purchase totals =	$1,020.43		$1,108.1753	$1,108.19	$1,108.25	$1,108.10