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	$10.57	12.656%	$11.9077	$11.91	$11.90	$11.90
Purchase #2	$38.56	11.320%	$42.925	$42.93	$42.95	$42.90
Purchase #3	$55.63	6.107%	$59.0273	$59.03	$59.05	$59.00
Purchase #4	$115.85	11.864%	$129.5944	$129.59	$129.60	$129.60
Purchase #5	$242.96	10.713%	$268.9883	$268.99	$269.00	$269.00
Purchase #6	$239.81	6.438%	$255.249	$255.25	$255.25	$255.20
Purchase #7	$93.37	7.329%	$100.2131	$100.21	$100.20	$100.20
7 purchase totals =	$796.75		$867.9048	$867.91	$867.95	$867.80