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	$90.57	11.430%	$100.9222	$100.92	$100.90	$100.90
Purchase #2	$166.78	7.268%	$178.9016	$178.90	$178.90	$178.90
Purchase #3	$161.33	13.617%	$183.2983	$183.30	$183.30	$183.30
Purchase #4	$174.63	6.454%	$185.9006	$185.90	$185.90	$185.90
Purchase #5	$164.70	11.613%	$183.8266	$183.83	$183.85	$183.80
Purchase #6	$37.97	12.299%	$42.6399	$42.64	$42.65	$42.60
Purchase #7	$168.45	5.456%	$177.6406	$177.64	$177.65	$177.60
7 purchase totals =	$964.43		$1,053.1298	$1,053.13	$1,053.15	$1,053.00