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	$228.75	12.596%	$257.5634	$257.56	$257.55	$257.60
Purchase #2	$68.48	6.470%	$72.9107	$72.91	$72.90	$72.90
Purchase #3	$58.31	10.378%	$64.3614	$64.36	$64.35	$64.40
Purchase #4	$174.57	12.541%	$196.4628	$196.46	$196.45	$196.50
Purchase #5	$32.75	6.622%	$34.9187	$34.92	$34.90	$34.90
Purchase #6	$187.94	13.185%	$212.7199	$212.72	$212.70	$212.70
Purchase #7	$72.38	8.760%	$78.7205	$78.72	$78.70	$78.70
7 purchase totals =	$823.18		$917.6574	$917.65	$917.55	$917.70