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	$183.36	12.803%	$206.8356	$206.84	$206.85	$206.80
Purchase #2	$72.52	6.525%	$77.2519	$77.25	$77.25	$77.30
Purchase #3	$168.70	10.330%	$186.1267	$186.13	$186.15	$186.10
Purchase #4	$103.58	5.293%	$109.0625	$109.06	$109.05	$109.10
Purchase #5	$178.95	9.673%	$196.2598	$196.26	$196.25	$196.30
Purchase #6	$169.50	12.410%	$190.535	$190.54	$190.55	$190.50
Purchase #7	$14.52	6.336%	$15.44	$15.44	$15.45	$15.40
7 purchase totals =	$891.13		$981.5115	$981.52	$981.55	$981.50