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	$75.28	11.146%	$83.6707	$83.67	$83.65	$83.70
Purchase #2	$61.88	5.654%	$65.3787	$65.38	$65.40	$65.40
Purchase #3	$105.36	4.280%	$109.8694	$109.87	$109.85	$109.90
Purchase #4	$131.27	7.810%	$141.5222	$141.52	$141.50	$141.50
Purchase #5	$95.70	3.430%	$98.9825	$98.98	$99.00	$99.00
Purchase #6	$153.54	11.848%	$171.7314	$171.73	$171.75	$171.70
Purchase #7	$218.30	5.781%	$230.9199	$230.92	$230.90	$230.90
7 purchase totals =	$841.33		$902.0748	$902.07	$902.05	$902.10