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	$6.87	9.344%	$7.5119	$7.51	$7.50	$7.50
Purchase #2	$167.63	3.684%	$173.8055	$173.81	$173.80	$173.80
Purchase #3	$37.36	7.221%	$40.0578	$40.06	$40.05	$40.10
Purchase #4	$79.48	13.322%	$90.0683	$90.07	$90.05	$90.10
Purchase #5	$182.85	5.314%	$192.5666	$192.57	$192.55	$192.60
Purchase #6	$27.40	5.297%	$28.8514	$28.85	$28.85	$28.90
Purchase #7	$29.52	6.230%	$31.3591	$31.36	$31.35	$31.40
7 purchase totals =	$531.11		$564.2206	$564.23	$564.15	$564.40