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	$50.54	9.510%	$55.3464	$55.35	$55.35	$55.30
Purchase #2	$64.43	13.181%	$72.9225	$72.92	$72.90	$72.90
Purchase #3	$57.29	13.631%	$65.0992	$65.10	$65.10	$65.10
Purchase #4	$76.33	7.618%	$82.1448	$82.14	$82.15	$82.10
Purchase #5	$136.51	3.271%	$140.9752	$140.98	$141.00	$141.00
Purchase #6	$29.28	13.593%	$33.26	$33.26	$33.25	$33.30
Purchase #7	$71.90	9.222%	$78.5306	$78.53	$78.55	$78.50
7 purchase totals =	$486.28		$528.2787	$528.28	$528.30	$528.20