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	$102.59	4.509%	$107.2158	$107.22	$107.20	$107.20
Purchase #2	$236.89	13.430%	$268.7043	$268.70	$268.70	$268.70
Purchase #3	$88.37	8.678%	$96.0387	$96.04	$96.05	$96.00
Purchase #4	$101.86	7.479%	$109.4781	$109.48	$109.50	$109.50
Purchase #5	$122.85	13.384%	$139.2922	$139.29	$139.30	$139.30
Purchase #6	$94.31	12.157%	$105.7753	$105.78	$105.80	$105.80
Purchase #7	$102.40	13.213%	$115.9301	$115.93	$115.95	$115.90
7 purchase totals =	$849.27		$942.4345	$942.44	$942.50	$942.40