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	$110.49	12.155%	$123.9201	$123.92	$123.90	$123.90
Purchase #2	$184.40	11.112%	$204.8905	$204.89	$204.90	$204.90
Purchase #3	$160.44	7.417%	$172.3398	$172.34	$172.35	$172.30
Purchase #4	$244.38	4.838%	$256.2031	$256.20	$256.20	$256.20
Purchase #5	$56.32	5.618%	$59.4841	$59.48	$59.50	$59.50
Purchase #6	$200.27	13.536%	$227.3785	$227.38	$227.40	$227.40
Purchase #7	$230.63	4.802%	$241.7049	$241.70	$241.70	$241.70
7 purchase totals =	$1,186.93		$1,285.9210	$1,285.91	$1,285.95	$1,285.90