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	$234.94	13.807%	$267.3782	$267.38	$267.40	$267.40
Purchase #2	$105.54	7.362%	$113.3099	$113.31	$113.30	$113.30
Purchase #3	$217.72	6.477%	$231.8217	$231.82	$231.80	$231.80
Purchase #4	$157.64	5.405%	$166.1604	$166.16	$166.15	$166.20
Purchase #5	$33.53	12.264%	$37.6421	$37.64	$37.65	$37.60
Purchase #6	$231.95	4.399%	$242.1535	$242.15	$242.15	$242.20
Purchase #7	$160.56	4.827%	$168.3102	$168.31	$168.30	$168.30
7 purchase totals =	$1,141.88		$1,226.7760	$1,226.77	$1,226.75	$1,226.80