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	$93.98	11.273%	$104.5744	$104.57	$104.55	$104.60
Purchase #2	$133.87	12.215%	$150.2222	$150.22	$150.20	$150.20
Purchase #3	$37.95	6.807%	$40.5333	$40.53	$40.55	$40.50
Purchase #4	$92.63	12.737%	$104.4283	$104.43	$104.45	$104.40
Purchase #5	$36.89	6.159%	$39.1621	$39.16	$39.15	$39.20
Purchase #6	$200.51	13.150%	$226.8771	$226.88	$226.90	$226.90
Purchase #7	$226.37	5.148%	$238.0235	$238.02	$238.00	$238.00
7 purchase totals =	$822.20		$903.8209	$903.81	$903.80	$903.80