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	$230.39	4.830%	$241.5178	$241.52	$241.50	$241.50
Purchase #2	$79.55	8.717%	$86.4844	$86.48	$86.50	$86.50
Purchase #3	$198.56	13.223%	$224.8156	$224.82	$224.80	$224.80
Purchase #4	$127.63	10.752%	$141.3528	$141.35	$141.35	$141.40
Purchase #5	$92.67	8.850%	$100.8713	$100.87	$100.85	$100.90
Purchase #6	$6.28	6.229%	$6.6712	$6.67	$6.65	$6.70
Purchase #7	$34.78	7.263%	$37.3061	$37.31	$37.30	$37.30
7 purchase totals =	$769.86		$839.0192	$839.02	$838.95	$839.10