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	$247.33	13.357%	$280.3659	$280.37	$280.35	$280.40
Purchase #2	$45.54	4.725%	$47.6918	$47.69	$47.70	$47.70
Purchase #3	$190.95	12.445%	$214.7137	$214.71	$214.70	$214.70
Purchase #4	$24.54	7.448%	$26.3677	$26.37	$26.35	$26.40
Purchase #5	$232.94	13.853%	$265.2092	$265.21	$265.20	$265.20
Purchase #6	$97.57	12.624%	$109.8872	$109.89	$109.90	$109.90
Purchase #7	$92.40	7.799%	$99.6063	$99.61	$99.60	$99.60
7 purchase totals =	$931.27		$1,043.8418	$1,043.85	$1,043.80	$1,043.90