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	$154.94	8.793%	$168.5639	$168.56	$168.55	$168.60
Purchase #2	$218.55	11.351%	$243.3576	$243.36	$243.35	$243.40
Purchase #3	$59.90	13.757%	$68.1404	$68.14	$68.15	$68.10
Purchase #4	$198.32	10.742%	$219.6235	$219.62	$219.60	$219.60
Purchase #5	$35.60	12.589%	$40.0817	$40.08	$40.10	$40.10
Purchase #6	$72.25	7.444%	$77.6283	$77.63	$77.65	$77.60
Purchase #7	$206.40	7.800%	$222.4992	$222.50	$222.50	$222.50
7 purchase totals =	$945.96		$1,039.8946	$1,039.89	$1,039.90	$1,039.90