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	$70.32	6.840%	$75.1299	$75.13	$75.15	$75.10
Purchase #2	$73.80	12.500%	$83.025	$83.03	$83.05	$83.00
Purchase #3	$141.40	5.107%	$148.6213	$148.62	$148.60	$148.60
Purchase #4	$196.84	5.121%	$206.9202	$206.92	$206.90	$206.90
Purchase #5	$244.85	9.808%	$268.8649	$268.86	$268.85	$268.90
Purchase #6	$133.95	7.411%	$143.877	$143.88	$143.90	$143.90
Purchase #7	$167.80	3.439%	$173.5706	$173.57	$173.55	$173.60
7 purchase totals =	$1,028.96		$1,100.0089	$1,100.01	$1,100.00	$1,100.00