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	$114.43	5.338%	$120.5383	$120.54	$120.55	$120.50
Purchase #2	$111.80	12.185%	$125.4228	$125.42	$125.40	$125.40
Purchase #3	$96.38	3.719%	$99.9644	$99.96	$99.95	$100.00
Purchase #4	$154.65	8.665%	$168.0504	$168.05	$168.05	$168.10
Purchase #5	$88.93	11.353%	$99.0262	$99.03	$99.05	$99.00
Purchase #6	$92.78	4.523%	$96.9764	$96.98	$97.00	$97.00
Purchase #7	$140.29	12.814%	$158.2668	$158.27	$158.25	$158.30
7 purchase totals =	$799.26		$868.2453	$868.25	$868.25	$868.30