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	$5.35	7.531%	$5.7529	$5.75	$5.75	$5.80
Purchase #2	$242.95	4.347%	$253.511	$253.51	$253.50	$253.50
Purchase #3	$84.81	7.179%	$90.8985	$90.90	$90.90	$90.90
Purchase #4	$199.49	6.184%	$211.8265	$211.83	$211.85	$211.80
Purchase #5	$226.98	10.587%	$251.0104	$251.01	$251.00	$251.00
Purchase #6	$222.98	11.111%	$247.7553	$247.76	$247.75	$247.80
Purchase #7	$72.74	12.813%	$82.0602	$82.06	$82.05	$82.10
7 purchase totals =	$1,055.30		$1,142.8148	$1,142.82	$1,142.80	$1,142.90