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	$156.78	9.371%	$171.4719	$171.47	$171.45	$171.50
Purchase #2	$10.73	7.583%	$11.5437	$11.54	$11.55	$11.50
Purchase #3	$219.48	3.360%	$226.8545	$226.85	$226.85	$226.90
Purchase #4	$89.25	11.526%	$99.537	$99.54	$99.55	$99.50
Purchase #5	$11.42	7.311%	$12.2549	$12.25	$12.25	$12.30
Purchase #6	$232.59	3.703%	$241.2028	$241.20	$241.20	$241.20
Purchase #7	$82.63	10.136%	$91.0054	$91.01	$91.00	$91.00
7 purchase totals =	$802.88		$853.8702	$853.86	$853.85	$853.90