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	$155.61	13.263%	$176.2486	$176.25	$176.25	$176.20
Purchase #2	$82.67	3.262%	$85.3667	$85.37	$85.35	$85.40
Purchase #3	$27.49	11.330%	$30.6046	$30.60	$30.60	$30.60
Purchase #4	$87.45	12.643%	$98.5063	$98.51	$98.50	$98.50
Purchase #5	$91.33	7.271%	$97.9706	$97.97	$97.95	$98.00
Purchase #6	$42.79	7.247%	$45.891	$45.89	$45.90	$45.90
Purchase #7	$99.36	13.267%	$112.5421	$112.54	$112.55	$112.50
7 purchase totals =	$586.70		$647.1299	$647.13	$647.10	$647.10