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	$152.66	3.708%	$158.3206	$158.32	$158.30	$158.30
Purchase #2	$40.43	7.249%	$43.3608	$43.36	$43.35	$43.40
Purchase #3	$40.58	13.762%	$46.1646	$46.16	$46.15	$46.20
Purchase #4	$100.86	7.850%	$108.7775	$108.78	$108.80	$108.80
Purchase #5	$147.38	10.232%	$162.4599	$162.46	$162.45	$162.50
Purchase #6	$97.98	12.179%	$109.913	$109.91	$109.90	$109.90
Purchase #7	$197.67	11.542%	$220.4851	$220.49	$220.50	$220.50
7 purchase totals =	$777.56		$849.4815	$849.48	$849.45	$849.60