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	$27.61	4.612%	$28.8834	$28.88	$28.90	$28.90
Purchase #2	$62.81	3.507%	$65.0127	$65.01	$65.00	$65.00
Purchase #3	$184.57	3.221%	$190.515	$190.52	$190.50	$190.50
Purchase #4	$31.66	3.788%	$32.8593	$32.86	$32.85	$32.90
Purchase #5	$115.38	12.587%	$129.9029	$129.90	$129.90	$129.90
Purchase #6	$14.68	7.672%	$15.8062	$15.81	$15.80	$15.80
Purchase #7	$243.51	10.648%	$269.4389	$269.44	$269.45	$269.40
7 purchase totals =	$680.22		$732.4184	$732.42	$732.40	$732.40