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	$105.28	3.701%	$109.1764	$109.18	$109.20	$109.20
Purchase #2	$84.47	5.445%	$89.0694	$89.07	$89.05	$89.10
Purchase #3	$215.39	6.792%	$230.0193	$230.02	$230.00	$230.00
Purchase #4	$82.64	7.564%	$88.8909	$88.89	$88.90	$88.90
Purchase #5	$179.57	5.540%	$189.5182	$189.52	$189.50	$189.50
Purchase #6	$52.93	5.780%	$55.9894	$55.99	$56.00	$56.00
Purchase #7	$55.76	12.110%	$62.5125	$62.51	$62.50	$62.50
7 purchase totals =	$776.04		$825.1761	$825.18	$825.15	$825.20