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	$89.81	10.229%	$98.9967	$99.00	$99.00	$99.00
Purchase #2	$123.29	13.130%	$139.478	$139.48	$139.50	$139.50
Purchase #3	$99.83	5.171%	$104.9922	$104.99	$105.00	$105.00
Purchase #4	$167.37	6.324%	$177.9545	$177.95	$177.95	$178.00
Purchase #5	$179.50	10.498%	$198.3439	$198.34	$198.35	$198.30
Purchase #6	$213.33	13.450%	$242.0229	$242.02	$242.00	$242.00
Purchase #7	$133.41	12.280%	$149.7927	$149.79	$149.80	$149.80
7 purchase totals =	$1,006.54		$1,111.5809	$1,111.57	$1,111.60	$1,111.60