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	$230.90	6.142%	$245.0819	$245.08	$245.10	$245.10
Purchase #2	$86.86	13.868%	$98.9057	$98.91	$98.90	$98.90
Purchase #3	$42.93	6.793%	$45.8462	$45.85	$45.85	$45.80
Purchase #4	$71.47	4.237%	$74.4982	$74.50	$74.50	$74.50
Purchase #5	$72.45	7.727%	$78.0482	$78.05	$78.05	$78.00
Purchase #6	$75.30	8.836%	$81.9535	$81.95	$81.95	$82.00
Purchase #7	$143.79	6.184%	$152.682	$152.68	$152.70	$152.70
7 purchase totals =	$723.70		$777.0157	$777.02	$777.05	$777.00