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	$209.90	4.547%	$219.4442	$219.44	$219.45	$219.40
Purchase #2	$109.32	12.797%	$123.3097	$123.31	$123.30	$123.30
Purchase #3	$106.26	11.752%	$118.7477	$118.75	$118.75	$118.70
Purchase #4	$91.79	3.414%	$94.9237	$94.92	$94.90	$94.90
Purchase #5	$22.66	13.602%	$25.7422	$25.74	$25.75	$25.70
Purchase #6	$142.25	9.787%	$156.172	$156.17	$156.15	$156.20
Purchase #7	$219.55	9.490%	$240.3853	$240.39	$240.40	$240.40
7 purchase totals =	$901.73		$978.7248	$978.72	$978.70	$978.60