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	$192.40	3.111%	$198.3856	$198.39	$198.40	$198.40
Purchase #2	$138.73	9.124%	$151.3877	$151.39	$151.40	$151.40
Purchase #3	$131.31	10.213%	$144.7207	$144.72	$144.70	$144.70
Purchase #4	$82.46	5.574%	$87.0563	$87.06	$87.05	$87.10
Purchase #5	$78.27	9.213%	$85.481	$85.48	$85.50	$85.50
Purchase #6	$61.26	10.235%	$67.53	$67.53	$67.55	$67.50
Purchase #7	$67.72	3.296%	$69.9521	$69.95	$69.95	$70.00
7 purchase totals =	$752.15		$804.5134	$804.52	$804.55	$804.60