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	$155.47	11.369%	$173.1454	$173.15	$173.15	$173.10
Purchase #2	$36.41	4.515%	$38.0539	$38.05	$38.05	$38.10
Purchase #3	$162.57	12.504%	$182.8978	$182.90	$182.90	$182.90
Purchase #4	$188.94	5.281%	$198.9179	$198.92	$198.90	$198.90
Purchase #5	$137.34	4.536%	$143.5697	$143.57	$143.55	$143.60
Purchase #6	$28.85	13.820%	$32.8371	$32.84	$32.85	$32.80
Purchase #7	$208.71	12.610%	$235.0283	$235.03	$235.05	$235.00
7 purchase totals =	$918.29		$1,004.4501	$1,004.46	$1,004.45	$1,004.40