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	$55.40	8.111%	$59.8935	$59.89	$59.90	$59.90
Purchase #2	$85.86	7.206%	$92.0471	$92.05	$92.05	$92.00
Purchase #3	$161.54	11.131%	$179.521	$179.52	$179.50	$179.50
Purchase #4	$71.64	10.223%	$78.9638	$78.96	$78.95	$79.00
Purchase #5	$119.30	13.138%	$134.9736	$134.97	$134.95	$135.00
Purchase #6	$43.56	12.508%	$49.0085	$49.01	$49.00	$49.00
Purchase #7	$207.47	5.142%	$218.1381	$218.14	$218.15	$218.10
7 purchase totals =	$744.77		$812.5456	$812.54	$812.50	$812.50