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	$247.50	12.282%	$277.898	$277.90	$277.90	$277.90
Purchase #2	$137.94	6.483%	$146.8827	$146.88	$146.90	$146.90
Purchase #3	$132.86	3.372%	$137.34	$137.34	$137.35	$137.30
Purchase #4	$80.49	3.302%	$83.1478	$83.15	$83.15	$83.10
Purchase #5	$71.97	11.535%	$80.2717	$80.27	$80.25	$80.30
Purchase #6	$177.37	13.302%	$200.9638	$200.96	$200.95	$201.00
Purchase #7	$111.83	13.578%	$127.0143	$127.01	$127.00	$127.00
7 purchase totals =	$959.96		$1,053.5183	$1,053.51	$1,053.50	$1,053.50