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	$140.50	11.669%	$156.8949	$156.89	$156.90	$156.90
Purchase #2	$61.89	11.536%	$69.0296	$69.03	$69.05	$69.00
Purchase #3	$135.28	8.171%	$146.3337	$146.33	$146.35	$146.30
Purchase #4	$222.49	9.616%	$243.8846	$243.88	$243.90	$243.90
Purchase #5	$177.33	8.568%	$192.5236	$192.52	$192.50	$192.50
Purchase #6	$74.72	4.712%	$78.2408	$78.24	$78.25	$78.20
Purchase #7	$85.36	9.483%	$93.4547	$93.45	$93.45	$93.50
7 purchase totals =	$897.57		$980.3619	$980.34	$980.40	$980.30