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	$171.96	12.764%	$193.909	$193.91	$193.90	$193.90
Purchase #2	$223.41	3.405%	$231.0171	$231.02	$231.00	$231.00
Purchase #3	$239.58	6.826%	$255.9337	$255.93	$255.95	$255.90
Purchase #4	$140.38	9.360%	$153.5196	$153.52	$153.50	$153.50
Purchase #5	$103.57	8.749%	$112.6313	$112.63	$112.65	$112.60
Purchase #6	$171.59	4.795%	$179.8177	$179.82	$179.80	$179.80
Purchase #7	$192.89	13.645%	$219.2098	$219.21	$219.20	$219.20
7 purchase totals =	$1,243.38		$1,346.0382	$1,346.04	$1,346.00	$1,345.90