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	$44.44	11.580%	$49.5862	$49.59	$49.60	$49.60
Purchase #2	$211.88	13.367%	$240.202	$240.20	$240.20	$240.20
Purchase #3	$56.47	11.147%	$62.7647	$62.76	$62.75	$62.80
Purchase #4	$49.66	11.755%	$55.4975	$55.50	$55.50	$55.50
Purchase #5	$72.84	12.813%	$82.173	$82.17	$82.15	$82.20
Purchase #6	$99.43	8.425%	$107.807	$107.81	$107.80	$107.80
Purchase #7	$189.25	3.718%	$196.2863	$196.29	$196.30	$196.30
7 purchase totals =	$723.97		$794.3167	$794.32	$794.30	$794.40