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	$128.41	12.398%	$144.3303	$144.33	$144.35	$144.30
Purchase #2	$100.31	4.190%	$104.513	$104.51	$104.50	$104.50
Purchase #3	$48.77	7.711%	$52.5307	$52.53	$52.55	$52.50
Purchase #4	$62.98	4.531%	$65.8336	$65.83	$65.85	$65.80
Purchase #5	$38.38	8.310%	$41.5694	$41.57	$41.55	$41.60
Purchase #6	$209.34	4.738%	$219.2585	$219.26	$219.25	$219.30
Purchase #7	$94.35	3.307%	$97.4702	$97.47	$97.45	$97.50
7 purchase totals =	$682.54		$725.5057	$725.50	$725.50	$725.50