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	$12.68	6.843%	$13.5477	$13.55	$13.55	$13.50
Purchase #2	$236.63	6.395%	$251.7625	$251.76	$251.75	$251.80
Purchase #3	$91.49	8.759%	$99.5036	$99.50	$99.50	$99.50
Purchase #4	$212.28	3.195%	$219.0623	$219.06	$219.05	$219.10
Purchase #5	$82.89	13.522%	$94.0984	$94.10	$94.10	$94.10
Purchase #6	$19.74	11.150%	$21.941	$21.94	$21.95	$21.90
Purchase #7	$65.25	9.671%	$71.5603	$71.56	$71.55	$71.60
7 purchase totals =	$720.96		$771.4758	$771.47	$771.45	$771.50