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	$12.92	5.580%	$13.6409	$13.64	$13.65	$13.60
Purchase #2	$113.92	10.203%	$125.5433	$125.54	$125.55	$125.50
Purchase #3	$175.98	6.217%	$186.9207	$186.92	$186.90	$186.90
Purchase #4	$171.60	3.362%	$177.3692	$177.37	$177.35	$177.40
Purchase #5	$79.41	12.589%	$89.4069	$89.41	$89.40	$89.40
Purchase #6	$20.61	4.546%	$21.5469	$21.55	$21.55	$21.50
Purchase #7	$95.76	5.280%	$100.8161	$100.82	$100.80	$100.80
7 purchase totals =	$670.20		$715.2440	$715.25	$715.20	$715.10