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	$154.94	12.253%	$173.9248	$173.92	$173.90	$173.90
Purchase #2	$158.77	9.350%	$173.615	$173.62	$173.60	$173.60
Purchase #3	$83.30	11.870%	$93.1877	$93.19	$93.20	$93.20
Purchase #4	$33.56	10.107%	$36.9519	$36.95	$36.95	$37.00
Purchase #5	$187.40	4.771%	$196.3409	$196.34	$196.35	$196.30
Purchase #6	$81.86	5.145%	$86.0717	$86.07	$86.05	$86.10
Purchase #7	$79.66	4.851%	$83.5243	$83.52	$83.50	$83.50
7 purchase totals =	$779.49		$843.6163	$843.61	$843.55	$843.60