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	$38.32	4.460%	$40.0291	$40.03	$40.05	$40.00
Purchase #2	$76.27	9.140%	$83.2411	$83.24	$83.25	$83.20
Purchase #3	$245.41	10.151%	$270.3216	$270.32	$270.30	$270.30
Purchase #4	$36.67	10.457%	$40.5046	$40.50	$40.50	$40.50
Purchase #5	$121.49	6.538%	$129.433	$129.43	$129.45	$129.40
Purchase #6	$109.39	13.378%	$124.0242	$124.02	$124.00	$124.00
Purchase #7	$91.52	9.138%	$99.8831	$99.88	$99.90	$99.90
7 purchase totals =	$719.07		$787.4367	$787.42	$787.45	$787.30