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	$94.74	5.446%	$99.8995	$99.90	$99.90	$99.90
Purchase #2	$123.73	6.312%	$131.5398	$131.54	$131.55	$131.50
Purchase #3	$151.61	11.192%	$168.5782	$168.58	$168.60	$168.60
Purchase #4	$206.47	13.406%	$234.1494	$234.15	$234.15	$234.10
Purchase #5	$131.30	12.452%	$147.6495	$147.65	$147.65	$147.60
Purchase #6	$234.29	10.812%	$259.6214	$259.62	$259.60	$259.60
Purchase #7	$70.54	6.785%	$75.3261	$75.33	$75.35	$75.30
7 purchase totals =	$1,012.68		$1,116.7639	$1,116.77	$1,116.80	$1,116.60