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	$27.46	13.320%	$31.1177	$31.12	$31.10	$31.10
Purchase #2	$162.90	12.203%	$182.7787	$182.78	$182.80	$182.80
Purchase #3	$211.71	3.724%	$219.5941	$219.59	$219.60	$219.60
Purchase #4	$230.48	10.814%	$255.4041	$255.40	$255.40	$255.40
Purchase #5	$94.38	4.741%	$98.8546	$98.85	$98.85	$98.90
Purchase #6	$74.73	8.549%	$81.1187	$81.12	$81.10	$81.10
Purchase #7	$130.28	7.449%	$139.9846	$139.98	$140.00	$140.00
7 purchase totals =	$931.94		$1,008.8525	$1,008.84	$1,008.85	$1,008.90