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	$99.37	11.813%	$111.1086	$111.11	$111.10	$111.10
Purchase #2	$34.63	8.310%	$37.5078	$37.51	$37.50	$37.50
Purchase #3	$209.36	3.868%	$217.458	$217.46	$217.45	$217.50
Purchase #4	$247.76	10.210%	$273.0563	$273.06	$273.05	$273.10
Purchase #5	$57.56	10.353%	$63.5192	$63.52	$63.50	$63.50
Purchase #6	$227.58	11.154%	$252.9643	$252.96	$252.95	$253.00
Purchase #7	$96.99	7.154%	$103.9287	$103.93	$103.95	$103.90
7 purchase totals =	$973.25		$1,059.5429	$1,059.55	$1,059.50	$1,059.60