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	$230.28	12.677%	$259.4726	$259.47	$259.45	$259.50
Purchase #2	$144.90	9.740%	$159.0133	$159.01	$159.00	$159.00
Purchase #3	$6.27	12.578%	$7.0586	$7.06	$7.05	$7.10
Purchase #4	$65.66	9.539%	$71.9233	$71.92	$71.90	$71.90
Purchase #5	$153.58	11.238%	$170.8393	$170.84	$170.85	$170.80
Purchase #6	$132.79	8.529%	$144.1157	$144.12	$144.10	$144.10
Purchase #7	$94.34	9.678%	$103.4702	$103.47	$103.45	$103.50
7 purchase totals =	$827.82		$915.8930	$915.89	$915.80	$915.90