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	$150.67	7.448%	$161.8919	$161.89	$161.90	$161.90
Purchase #2	$246.55	9.814%	$270.7464	$270.75	$270.75	$270.70
Purchase #3	$65.27	13.169%	$73.8654	$73.87	$73.85	$73.90
Purchase #4	$36.98	9.656%	$40.5508	$40.55	$40.55	$40.60
Purchase #5	$83.69	13.638%	$95.1036	$95.10	$95.10	$95.10
Purchase #6	$59.61	7.251%	$63.9323	$63.93	$63.95	$63.90
Purchase #7	$65.69	9.826%	$72.1447	$72.14	$72.15	$72.10
7 purchase totals =	$708.46		$778.2351	$778.23	$778.25	$778.20