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	$250.76	11.239%	$278.9429	$278.94	$278.95	$278.90
Purchase #2	$239.86	4.484%	$250.6153	$250.62	$250.60	$250.60
Purchase #3	$135.93	4.378%	$141.881	$141.88	$141.90	$141.90
Purchase #4	$224.50	8.307%	$243.1492	$243.15	$243.15	$243.10
Purchase #5	$216.90	4.152%	$225.9057	$225.91	$225.90	$225.90
Purchase #6	$74.41	5.152%	$78.2436	$78.24	$78.25	$78.20
Purchase #7	$158.76	10.320%	$175.144	$175.14	$175.15	$175.10
7 purchase totals =	$1,301.12		$1,393.8817	$1,393.88	$1,393.90	$1,393.70