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	$202.97	7.565%	$218.3247	$218.32	$218.30	$218.30
Purchase #2	$79.73	13.818%	$90.7471	$90.75	$90.75	$90.70
Purchase #3	$10.29	3.494%	$10.6495	$10.65	$10.65	$10.60
Purchase #4	$142.73	9.810%	$156.7318	$156.73	$156.75	$156.70
Purchase #5	$116.91	5.674%	$123.5435	$123.54	$123.55	$123.50
Purchase #6	$161.40	12.727%	$181.9414	$181.94	$181.95	$181.90
Purchase #7	$101.32	9.574%	$111.0204	$111.02	$111.00	$111.00
7 purchase totals =	$815.35		$892.9584	$892.95	$892.95	$892.70