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	$95.25	12.556%	$107.2096	$107.21	$107.20	$107.20
Purchase #2	$55.27	5.705%	$58.4232	$58.42	$58.40	$58.40
Purchase #3	$131.90	3.762%	$136.8621	$136.86	$136.85	$136.90
Purchase #4	$240.32	12.245%	$269.7472	$269.75	$269.75	$269.70
Purchase #5	$41.81	3.192%	$43.1446	$43.14	$43.15	$43.10
Purchase #6	$238.58	5.303%	$251.2319	$251.23	$251.25	$251.20
Purchase #7	$186.76	7.257%	$200.3132	$200.31	$200.30	$200.30
7 purchase totals =	$989.89		$1,066.9318	$1,066.92	$1,066.90	$1,066.80