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	$162.98	11.118%	$181.1001	$181.10	$181.10	$181.10
Purchase #2	$165.77	10.520%	$183.209	$183.21	$183.20	$183.20
Purchase #3	$125.36	11.225%	$139.4317	$139.43	$139.45	$139.40
Purchase #4	$47.56	6.224%	$50.5201	$50.52	$50.50	$50.50
Purchase #5	$38.79	3.178%	$40.0227	$40.02	$40.00	$40.00
Purchase #6	$238.54	10.648%	$263.9397	$263.94	$263.95	$263.90
Purchase #7	$113.54	8.432%	$123.1137	$123.11	$123.10	$123.10
7 purchase totals =	$892.54		$981.3370	$981.33	$981.30	$981.20