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	$99.79	13.417%	$113.1788	$113.18	$113.20	$113.20
Purchase #2	$188.67	13.379%	$213.9122	$213.91	$213.90	$213.90
Purchase #3	$191.69	6.209%	$203.592	$203.59	$203.60	$203.60
Purchase #4	$162.64	9.672%	$178.3705	$178.37	$178.35	$178.40
Purchase #5	$79.64	13.779%	$90.6136	$90.61	$90.60	$90.60
Purchase #6	$29.33	10.577%	$32.4322	$32.43	$32.45	$32.40
Purchase #7	$51.60	5.443%	$54.4086	$54.41	$54.40	$54.40
7 purchase totals =	$803.36		$886.5079	$886.50	$886.50	$886.50