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	$149.72	12.762%	$168.8273	$168.83	$168.85	$168.80
Purchase #2	$38.44	10.366%	$42.4247	$42.42	$42.40	$42.40
Purchase #3	$178.51	11.701%	$199.3975	$199.40	$199.40	$199.40
Purchase #4	$37.25	10.453%	$41.1437	$41.14	$41.15	$41.10
Purchase #5	$239.47	12.804%	$270.1317	$270.13	$270.15	$270.10
Purchase #6	$235.84	3.814%	$244.8349	$244.83	$244.85	$244.80
Purchase #7	$236.39	8.691%	$256.9347	$256.93	$256.95	$256.90
7 purchase totals =	$1,115.62		$1,223.6945	$1,223.68	$1,223.75	$1,223.50