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	$157.99	4.279%	$164.7504	$164.75	$164.75	$164.80
Purchase #2	$150.36	9.623%	$164.8291	$164.83	$164.85	$164.80
Purchase #3	$200.96	10.756%	$222.5753	$222.58	$222.60	$222.60
Purchase #4	$153.87	4.332%	$160.5356	$160.54	$160.55	$160.50
Purchase #5	$116.40	12.804%	$131.3039	$131.30	$131.30	$131.30
Purchase #6	$130.82	8.627%	$142.1058	$142.11	$142.10	$142.10
Purchase #7	$180.38	13.616%	$204.9405	$204.94	$204.95	$204.90
7 purchase totals =	$1,090.78		$1,191.0406	$1,191.05	$1,191.10	$1,191.00