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	$155.65	11.480%	$173.5186	$173.52	$173.50	$173.50
Purchase #2	$138.99	9.527%	$152.2316	$152.23	$152.25	$152.20
Purchase #3	$202.55	6.835%	$216.3943	$216.39	$216.40	$216.40
Purchase #4	$146.99	12.461%	$165.3064	$165.31	$165.30	$165.30
Purchase #5	$77.54	7.393%	$83.2725	$83.27	$83.25	$83.30
Purchase #6	$30.57	6.507%	$32.5592	$32.56	$32.55	$32.60
Purchase #7	$188.55	3.258%	$194.693	$194.69	$194.70	$194.70
7 purchase totals =	$940.84		$1,017.9756	$1,017.97	$1,017.95	$1,018.00