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	$150.98	11.859%	$168.8847	$168.88	$168.90	$168.90
Purchase #2	$146.89	13.706%	$167.0227	$167.02	$167.00	$167.00
Purchase #3	$62.78	9.195%	$68.5526	$68.55	$68.55	$68.60
Purchase #4	$141.54	11.814%	$158.2615	$158.26	$158.25	$158.30
Purchase #5	$93.98	5.525%	$99.1724	$99.17	$99.15	$99.20
Purchase #6	$247.69	9.824%	$272.0231	$272.02	$272.00	$272.00
Purchase #7	$212.61	5.475%	$224.2504	$224.25	$224.25	$224.30
7 purchase totals =	$1,056.47		$1,158.1674	$1,158.15	$1,158.10	$1,158.30