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	$129.78	10.407%	$143.2862	$143.29	$143.30	$143.30
Purchase #2	$84.70	11.477%	$94.421	$94.42	$94.40	$94.40
Purchase #3	$136.59	3.153%	$140.8967	$140.90	$140.90	$140.90
Purchase #4	$65.85	3.145%	$67.921	$67.92	$67.90	$67.90
Purchase #5	$116.36	6.413%	$123.8222	$123.82	$123.80	$123.80
Purchase #6	$36.58	13.248%	$41.4261	$41.43	$41.45	$41.40
Purchase #7	$41.60	13.394%	$47.1719	$47.17	$47.15	$47.20
7 purchase totals =	$611.46		$658.9451	$658.95	$658.90	$658.90