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	$246.59	8.487%	$267.5181	$267.52	$267.50	$267.50
Purchase #2	$131.54	3.605%	$136.282	$136.28	$136.30	$136.30
Purchase #3	$120.83	6.676%	$128.8966	$128.90	$128.90	$128.90
Purchase #4	$78.97	11.489%	$88.0429	$88.04	$88.05	$88.00
Purchase #5	$209.80	4.151%	$218.5088	$218.51	$218.50	$218.50
Purchase #6	$162.42	5.540%	$171.4181	$171.42	$171.40	$171.40
Purchase #7	$129.33	6.298%	$137.4752	$137.48	$137.50	$137.50
7 purchase totals =	$1,079.48		$1,148.1417	$1,148.15	$1,148.15	$1,148.10