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	$100.55	11.254%	$111.8659	$111.87	$111.85	$111.90
Purchase #2	$110.69	11.614%	$123.5455	$123.55	$123.55	$123.50
Purchase #3	$171.76	13.297%	$194.5989	$194.60	$194.60	$194.60
Purchase #4	$219.79	13.520%	$249.5056	$249.51	$249.50	$249.50
Purchase #5	$250.57	11.483%	$279.343	$279.34	$279.35	$279.30
Purchase #6	$120.86	13.334%	$136.9755	$136.98	$137.00	$137.00
Purchase #7	$145.33	12.764%	$163.8799	$163.88	$163.90	$163.90
7 purchase totals =	$1,119.55		$1,259.7143	$1,259.73	$1,259.75	$1,259.70