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	$64.38	7.654%	$69.3076	$69.31	$69.30	$69.30
Purchase #2	$55.67	12.417%	$62.5825	$62.58	$62.60	$62.60
Purchase #3	$25.91	5.743%	$27.398	$27.40	$27.40	$27.40
Purchase #4	$172.39	11.360%	$191.9735	$191.97	$191.95	$192.00
Purchase #5	$205.96	7.860%	$222.1485	$222.15	$222.15	$222.10
Purchase #6	$132.53	6.370%	$140.9722	$140.97	$140.95	$141.00
Purchase #7	$100.98	4.114%	$105.1343	$105.13	$105.15	$105.10
7 purchase totals =	$757.82		$819.5166	$819.51	$819.50	$819.50