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	$163.41	9.540%	$178.9993	$179.00	$179.00	$179.00
Purchase #2	$55.31	10.451%	$61.0904	$61.09	$61.10	$61.10
Purchase #3	$163.44	12.615%	$184.058	$184.06	$184.05	$184.10
Purchase #4	$53.25	12.488%	$59.8999	$59.90	$59.90	$59.90
Purchase #5	$186.50	13.377%	$211.4481	$211.45	$211.45	$211.40
Purchase #6	$65.90	9.109%	$71.9028	$71.90	$71.90	$71.90
Purchase #7	$88.60	11.748%	$99.0087	$99.01	$99.00	$99.00
7 purchase totals =	$776.41		$866.4072	$866.41	$866.40	$866.40