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	$129.45	5.645%	$136.7575	$136.76	$136.75	$136.80
Purchase #2	$69.45	13.611%	$78.9028	$78.90	$78.90	$78.90
Purchase #3	$166.72	5.604%	$176.063	$176.06	$176.05	$176.10
Purchase #4	$85.76	10.246%	$94.547	$94.55	$94.55	$94.50
Purchase #5	$91.96	4.334%	$95.9455	$95.95	$95.95	$95.90
Purchase #6	$42.69	6.588%	$45.5024	$45.50	$45.50	$45.50
Purchase #7	$230.73	11.330%	$256.8717	$256.87	$256.85	$256.90
7 purchase totals =	$816.76		$884.5899	$884.59	$884.55	$884.60