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	$88.89	13.159%	$100.587	$100.59	$100.60	$100.60
Purchase #2	$129.73	10.386%	$143.2038	$143.20	$143.20	$143.20
Purchase #3	$181.90	7.762%	$196.0191	$196.02	$196.00	$196.00
Purchase #4	$188.63	12.175%	$211.5957	$211.60	$211.60	$211.60
Purchase #5	$135.77	3.322%	$140.2803	$140.28	$140.30	$140.30
Purchase #6	$250.46	8.271%	$271.1755	$271.18	$271.20	$271.20
Purchase #7	$124.77	9.762%	$136.95	$136.95	$136.95	$137.00
7 purchase totals =	$1,100.15		$1,199.8114	$1,199.82	$1,199.85	$1,199.90