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	$89.57	5.327%	$94.3414	$94.34	$94.35	$94.30
Purchase #2	$116.36	5.775%	$123.0798	$123.08	$123.10	$123.10
Purchase #3	$126.45	10.299%	$139.4731	$139.47	$139.45	$139.50
Purchase #4	$98.35	10.791%	$108.9629	$108.96	$108.95	$109.00
Purchase #5	$165.47	12.388%	$185.9684	$185.97	$185.95	$186.00
Purchase #6	$230.43	12.331%	$258.8443	$258.84	$258.85	$258.80
Purchase #7	$92.88	9.713%	$101.9014	$101.90	$101.90	$101.90
7 purchase totals =	$919.51		$1,012.5713	$1,012.56	$1,012.55	$1,012.60